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diff --git a/32598.txt b/32598.txt new file mode 100644 index 0000000..7bb6220 --- /dev/null +++ b/32598.txt @@ -0,0 +1,6351 @@ +The Project Gutenberg EBook of Earth and Sky Every Child Should Know, by +Julia Ellen Rogers + +This eBook is for the use of anyone anywhere at no cost and with +almost no restrictions whatsoever. You may copy it, give it away or +re-use it under the terms of the Project Gutenberg License included +with this eBook or online at www.gutenberg.org + + +Title: Earth and Sky Every Child Should Know + Easy studies of the earth and the stars for any time and place + +Author: Julia Ellen Rogers + +Release Date: May 30, 2010 [EBook #32598] + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK EARTH AND SKY *** + + + + +Produced by Juliet Sutherland, Christine D. and the Online +Distributed Proofreading Team at http://www.pgdp.net + + + + + + + + + +[Illustration: Pike's Peak, Colorado] + + EARTH and SKY EVERY + CHILD SHOULD KNOW + + EASY STUDIES OF THE EARTH AND THE + STARS FOR ANY TIME AND PLACE + +BY + +JULIA ELLEN ROGERS + + AUTHOR OF + "THE TREE BOOK," "THE SHELL BOOK," "KEY TO THE NATURE + LIBRARY," "TREES EVERY CHILD SHOULD KNOW." + + ILLUSTRATED BY + THIRTY-ONE PAGES OF PHOTOGRAPHS AND DRAWINGS + +[Illustration] + + NEW YORK + GROSSET & DUNLAP + PUBLISHERS + + COPYRIGHT, 1910, BY DOUBLEDAY, PAGE & COMPANY + + PUBLISHED, OCTOBER, 1910 + + ALL RIGHTS RESERVED, INCLUDING THAT OF TRANSLATION + INTO FOREIGN LANGUAGES, INCLUDING THE SCANDINAVIAN + + + + +ACKNOWLEDGMENTS + + +A number of the photographs in this volume are used by permission of the +American Museum of Natural History. The star maps and drawings of the +constellations are by Mrs. Jerome B. Thomas. The poem by Longfellow, +quoted in part, is with the permission of the publishers, Houghton, +Mifflin & Co. + + * * * * * + + + + +CONTENTS + + + _PART I. THE EARTH_ + + PAGE + + THE GREAT STONE BOOK 3 + + THE FOSSIL FISH 6 + + THE CRUST OF THE EARTH 9 + + WHAT IS THE EARTH MADE OF? 14 + + THE FIRST DRY LAND 22 + + A STUDY OF GRANITE 27 + + METAMORPHIC ROCKS 31 + + THE AIR IN MOTION 35 + + THE WORK OF THE WIND 44 + + RAIN IN SUMMER, _by Henry W. Longfellow_ 50 + + WHAT BECOMES OF THE RAIN? 51 + + THE SOIL IN FIELDS AND GARDENS 58 + + THE WORK OF EARTHWORMS 63 + + QUIET FORCES THAT DESTROY ROCKS 68 + + HOW ROCKS ARE MADE 72 + + GETTING ACQUAINTED WITH A RIVER 78 + + THE WAYS OF RIVERS 84 + + THE STORY OF A POND 90 + + THE RIDDLE OF THE LOST ROCKS 93 + + THE QUESTION ANSWERED 96 + + GLACIERS AMONG THE ALPS 98 + + THE GREAT ICE SHEET 104 + + FOLLOWING SOME LOST RIVERS 110 + + THE MAMMOTH CAVE OF KENTUCKY 114 + + LAND BUILDING BY RIVERS 121 + + THE MAKING OF MOUNTAINS 126 + + THE LAVA FLOOD OF THE NORTHWEST 130 + + THE FIRST LIVING THINGS 134 + + AN ANCIENT BEACH AT EBB TIDE 138 + + THE LIME ROCKS 147 + + THE AGE OF FISHES 152 + + KING COAL 155 + + HOW COAL WAS MADE 160 + + THE MOST USEFUL METAL 167 + + THE AGE OF REPTILES 175 + + THE AGE OF MAMMALS 180 + + THE HORSE AND HIS ANCESTORS 186 + + THE AGE OF MAN 194 + + + _PART II. THE SKY_ + + EVERY FAMILY A "STAR CLUB" 201 + + THE DIPPERS AND THE POLE STAR 207 + + CONSTELLATIONS YOU CAN ALWAYS SEE 213 + + WINTER CONSTELLATIONS 219 + + ORION, HIS DOGS, AND THE BULL 223 + + SEVEN FAMOUS CONSTELLATIONS 231 + + THE TWENTY BRIGHTEST STARS 239 + + HOW TO LEARN MORE 241 + + + + +ILLUSTRATIONS + + + Pike's Peak _Frontispiece_ + + FACING PAGE + + Sand Dunes in Arizona 44 + + Grand Canon of the Colorado 45 + + Castles Carved by Rain and Wind 52 + + Where All the Water Comes From 53 + + The Richest Gold and Silver Mines 72 + + Rocks Being Ground to Flour 73 + + A Pond Made by a Glacier 88 + + The Struggle Between a Stream and Its + Banks 89 + + Ripple Marks and Glacial Striae 102 + + Glacial Grooves and Markings 103 + + Crinoid and Ammonite 140 + + Fossil Corals, Coquina, Hippurite Limestone 141 + + Fossil Fish 152 + + Meteorite 153 + + Eocene Fish and Trilobite 156 + + How Coal Was Made 157 + + Banded Sandstone. Opalized Wood 176 + + Allosaurus 177 + + A Three-horned Dinosaur 178 + + Remains of Brontosaurus 179 + + Restoration of Brontosaurus 182 + + Ornitholestes, a Small Dinosaur 183 + + A Mammoth 186 + + An Ancestor of the Horse 187 + + Orion, His Dogs, and the Bull 214 + + Other Fanciful Sketches of Constellations 215 + + The Sky in Winter 244 + + The Sky in Spring 244 + + The Sky in Summer 244 + + The Sky in Autumn 244 + + + + +PART I + +THE EARTH + + * * * * * + + + + +THE GREAT STONE BOOK + + "The crust of our earth is a great cemetery where the rocks + are tombstones on which the buried dead have written their + own epitaphs. They tell us who they were, and when and where + they lived."--_Louis Agassiz._ + + +Deep in the ground, and high and dry on the sides of mountains, belts of +limestone and sandstone and slate lie on the ancient granite ribs of the +earth. They are the deposits of sand and mud that formed the shores of +ancient seas. The limestone is formed of the decayed shells of animal +forms that flourished in shallow bays along those shores. And all we +know about the life of these early days is read in the epitaphs written +on these stone tables. + +Under the stratified rocks, the granite foundations tell nothing of life +on the earth. But the sea rolled over them, and in it lived a great +variety of shellfish. Evidently the earliest fossil-bearing rocks were +worn away, for the rocks that now lie on the granite show not the +beginnings, but the high tide of life. The "lost interval" of which +geologists speak was a time when living forms were few in the sea. + +In the muddy bottoms of shallow, quiet bays lie the shells and skeletons +of the creatures that live their lives in those waters and die when they +grow old and feeble. We have seen the fiddler crabs by thousands on +such shores, young and old, lusty and feeble. We have seen the rocks +along another coast almost covered by the coiled shells of little gray +periwinkles, and big clumps of black mussels hanging on the piers and +wharfs. All these creatures die, at length, and their shells accumulate +on the shallow sea bottom. Who has not spent hours gathering dead shells +which the tide has thrown up on the beach? Who has not cut his foot on +the broken shells that lie in the sandy bottom we walk on whenever we go +into the surf to swim or bathe? + +Read downward from the surface toward the earth's centre-- + + +TABLE OF CONTENTS + + + ------+----------------------+-----------+----------------------- + Part | _Rock Systems_ | _Dominant | _Dominant Plants_ + | | Animals_ | + ------+----------------------+-----------+----------------------- + VII. | Recent | Man | Flowering kinds + |{ Quaternary | | + VI. | { Pliocene | Mammals | Early flowering + |{ Tertiary { Miocene | | + | { Eocene | | + V. | Mesozoic | Reptiles | Cycads + IV. | Carboniferous | Amphibians| Ferns and Conifers + III. | Devonian | Fishes | Ferns + II. | Silurian | Molluscs | Seaweeds + I. | Fire-formed | No life | No life + ------+----------------------+-----------+----------------------- + +It is by dying that the creatures of the sea write their epitaphs. The +mud or sand swallows them up. In time these submerged banks may be left +dry, and become beds of stone. Then some of the skeletons and shells +may be revealed in blocks of quarried stone, still perfect in form after +lying buried for thousands of years. + +The leaves of this great stone book are the layers of rock, laid down +under water. Between the leaves are pressed specimens--fossils of +animals and plants that have lived on the earth. + + + + +THE FOSSIL FISH + + +I remember seeing a flat piece of stone on a library table, with the +skeleton of a fish distinctly raised on one surface. The friend who +owned this strange-looking specimen told me that she found it in a stone +quarry. She brought home a large piece of the slate, and a stone-mason +cut out the block with the fish in it, and her souvenir made a useful +and interesting paper-weight. + +The story of that fish I heard with wonder, and have never forgotten. I +had never heard of fossil animals or plants until my good neighbour +talked about them. She showed me bits of stone with fern leaves pressed +into them. One piece of hard limestone was as full of little sea-shells +as it could possibly be. One ball of marble was a honeycombed pattern, +and called "fossil coral." + +The fossil fish was once alive, swimming in the sea, and feeding on the +things it liked to eat, as all happy fishes do. Near shore a river +poured its muddy water into the sea, and the sandy bottom was covered +with the mud that settled on it. At last the fish grew old, and perhaps +a trifle stupid about catching minnows. It died, and sank to the muddy +floor of the sea. Its horny bones were not dissolved by the water. They +remained, and the mud filtered in and filled all the spaces. Soon the +fish was buried completely by the sediment the river brought. + +Years, thousands of them, went by, and the layer of mud was so thick and +heavy above the skeleton of the fish that it bore a weight of tons +there, under the water. The close-packed mud became a stiff clay. After +more thousands of years, the sea no longer came so far ashore, for the +river had built up a great delta of land out of mud. The clay in which +the fish was hidden hardened into slate. Water crept down in the loose +upper layers, dissolving out salt and other minerals, and having harder +work to soak through, the lower it went. The water left some of the +minerals it had accumulated, calcium and silica and iron, in the lower +rock beds, making them harder than they were before, and heavier and +less porous. + +When the river gorge was cut through these layers of rock, the colour +and thickness of each kind were laid bare. Centuries after, perhaps +thousands of years, indeed, the quarrymen cut out the layers fit for +building stones, flags for walks and slates for roofing. In the +splitting of a flagstone, the long-buried skeleton of the fish came to +light. + +Under our feet the earth lies in layers. Under the soil lie loose beds +of clay and sand and gravel, and under these loose kinds of earth are +close-packed clays, sandstones, limestones, shales, often strangely +tilted away from the horizontal line, but variously fitted, one layer to +another. Under these rocks lie the foundations of the earth--the +fire-formed rocks, like granite. The depth of this original rock is +unknown. It is the substance out of which the earth is made, we think. +All the layered rocks are made of particles of the older ones, stolen by +wind and water, and finally deposited on the borders of lakes and seas. +So our rivers are doing to-day what they have always done--they are +tearing down rocks, grinding and sifting the fragments, and letting them +fall where the current of fresh water meets a great body of water that +is still, or has currents contrary to that of the river. + +Do you see a little dead fish in the water? It is on the way to become a +fossil, and the mud that sifts over it, to become a layer of slate. +Every seashore buries its dead in layers of sand and mud. + + + + +THE CRUST OF THE EARTH + + +It is hard to believe that our solid earth was once a ball of seething +liquid, like the red-hot iron that is poured out of the big clay cups +into the sand moulds at an iron foundry. But when a mountain like +Vesuvius sets up a mighty rumbling, and finally a mass of white-hot lava +bursts from the centre and streams down the sides, covering the +vineyards and olive orchards, and driving the people out of their homes +in terror, it seems as if the earth's crust must be but a thin and frail +affair, covering a fiery interior, which might at any time break out. +The people who live near volcanoes might easily get this idea. + +But they do not. They go back as soon as the lava streams are cooled, +and rebuild their homes, and plant more orchards and vineyards. "It is +_so_ many years," say they to one another, "since the last bad eruption. +Vesuvius will probably sleep now till we are dead and gone." + +This is good reasoning. There are few active volcanoes left on the +earth, compared with the number that were once active, and long ago +became extinct. And the time between eruptions of the active ones grows +longer; the eruptions less violent. Terrible as were the recent +earthquakes of San Francisco and Messina, this form of disturbance of +the earth's crust is growing constantly less frequent. The earth is +growing cooler as it grows older; the crust thickens and grows stronger +as centuries pass. We have been studying the earth only a few hundred +years. The crust has been cooling for millions of years, and +mountain-making was the result of the shrinking of the crust. That +formed folds and clefts, and let masses of the heated substance pour out +on the surface. + +My first geography lesson I shall never forget. The new teacher had very +bright eyes and _such_ pretty hands! She held up a red apple, and told +us that the earth's substance was melted and burning, inside its crust, +which was about as thick, in proportion to the size of the globe, as the +skin of the apple. I was filled with wonder and fear. What if we +children jumped the rope so hard as to break through the fragile shell, +and drop out of sight in a sea of fiery metal, like melted iron? Some of +the boys didn't believe it, but they were impressed, nevertheless. + +The theory of the heated interior of the earth is still believed, but +the idea that flames and bubbling metals are enclosed in the outer layer +of solid matter has generally been abandoned. The power that draws all +of its particles toward the earth's centre is stated by the laws of +gravitation. The amount of "pull" is the measure of the weight of any +substance. Lift a stone, and then a feather pillow, much larger than +the stone. One is strongly drawn to the earth; the other not. One is +_heavy_, we say, the other _light_. + +If a stone you can pick up is heavy, how much heavier is a great boulder +that it takes a four-horse team to haul. What tremendous weight there is +in all the boulders scattered on a hillside! The hill itself could not +be made level without digging away thousands of tons of earth. The +earth's outer crust, with its miles in depth of mountains and level +ground, is a crushing weight lying on the heated under-substance. Every +foot of depth adds greatly to the pressure exerted upon the mass, for +the attraction of gravitation increases amazingly as the centre of the +earth is approached. + +It is now believed that the earth is solid to its centre, though heated +to a high degree. Terrific pressure, which causes this heat, is exerted +by the weight of the crust. A crack in the crust may relieve this +pressure at some point, and a mass of substance may be forced out and +burst into a flaming stream of lava. Such an eruption is familiar in +volcanic regions. The fact that red-hot lava streams from the crater of +Vesuvius is no proof that it was seething and bubbling while far below +the surface. + +Volcanoes, geysers, and hot springs prove that the earth's interior is +hot. The crust is frozen the year around in the polar regions, and never +between the Tropics of Cancer and Capricorn. The sun's rays produce our +different climates, but they affect only the surface. Underground, there +is a rise of a degree of temperature for every fifty feet one goes +down. The lowest mine shaft is about a mile deep. That is only one +four-thousandth of the distance to the earth's centre. + +By an easy computation we could locate the known melting-point for +metals and other rock materials. But one degree for each fifty feet of +depth below the surface may not be correct for the second mile, as it is +for the first. Again, the melting-point is probably a great deal higher +for substances under great pressure. The weight of the crust is a burden +the under-rocks bear. Probably the pressure on every square inch reaches +thousands of tons. Could any substance become liquid with such a weight +upon it, whatever heat it attained? Nobody can answer this question. + +The theory that volcanoes are chimneys connecting lakes of burning lava +with the surface of the earth is discredited by geologists. The weight +of the overlying crust would, they think, close such chambers, and +reduce liquids to a solid condition. + +Since the first land rose above the sea, the crust of the earth has +gradually become more stable, but even now there is scarcely a day when +the instruments called seismographs do not record earthquake shocks in +some part of the earth; and the outbreaks of Vesuvius and AEtna, the +constant boiling of lava in the craters of the Hawaiian Islands and +other volcanic centres, prove that even now the earth's crust is very +thin and unstable. The further back in time we go, the thinner was the +crust, the more frequent the outbursts of volcanic activity, the more +readily did wrinkles form. + +The shores of New Jersey and of Greenland are gradually sinking, and the +sea coming up over the land. Certain parts of the world are gradually +rising out of the sea. In earlier times the rising or the sinking of +land over large areas happened much more frequently than now. + + + + +WHAT IS THE EARTH MADE OF? + + +"Baking day" is a great institution in the comfortable farm life of the +American people. The big range oven is not allowed to grow cold until +rows of pies adorn the pantry shelves, and cakes, tarts, and generous +loaves of bread are added to the store. Cookies, perhaps, and a big pan +full of crisp, brown doughnuts often crown the day's work. No gallery of +art treasures will ever charm the grown-up boys and girls as those +pantry shelves charmed the bright-eyed, hungry children, who were +allowed to survey the treasure-house, and sample its good things while +they were still warm. + +You could count a dozen different kinds of cakes and pies, rolls and +cookies on those pantry shelves, yet several of them were made out of +the same dough. Instead of a loaf of bread, mother could make two or +three kinds of coffee cake, or cinnamon rolls, or currant buns, or +Parker-House rolls. Even the pastry, which made the pies and tarts, was +not so different from the bread dough, for each was made of flour, and +contained, besides the salt, "shortening," which was butter or lard. +Sugar was used in everything, from the bread, which had a +table-spoonful, to the cookies, which were finished with a sifting of +sugar on top. + +How much of the food we eat is made of a very few staple +foodstuffs,--starch, sugar, fats! So in the wonderful earth and all that +grows out of it and lives upon it. Only seventy different elements have +been discovered, counting, besides the earth, the water and the air, and +even the strange wandering bodies, called meteorites, that fall upon the +earth out of the sky. Like the flour in the different cakes and pies, +the element carbon is found in abundance and in strangely different +combinations. As a gas, in combination with oxygen, it is breathed out +of our lungs, and out of chimneys where coal and wood are burned. It +forms a large part of the framework of trees and other plants, and +remains as charcoal when the wood is slowly burned under a close +covering. There is a good proportion of carbon in animal bodies, in the +bones as well as the soft parts, and carbon is plentiful in the mineral +substances of the earth. + +The chemist is the man who has determined for us the existence and the +distribution of the seventy elements. He finds them in the solid +substances of the globe and in the water that covers four-fifths of its +surface; in the atmosphere that covers sea and land, and in all the +living forms of plants and animals that live in the seas and on the +land. By means of an instrument called the spectroscope, the heavenly +bodies are proved to be made of the same substances that are found in +the rocks. The sun tells what it is made of, and one proof that the +earth is a child of the sun is in the fact that the same elements are +found in the substance of both. + +Of the seventy elements, the most important are these: Oxygen, silicon, +aluminum, iron, manganese, calcium, magnesium, potassium, sodium, +carbon, hydrogen, phosphorus, sulphur, chlorine, nitrogen. + +_Oxygen_ is the most plentiful and the most important element. One-fifth +of the air we breathe is oxygen; one-third of the water we drink. The +rock foundations of the earth are nearly one-half oxygen. No fire can +burn, no plant or animal can grow, or even decay after it dies, unless +oxygen is present and takes an active part in each process. Strangely +enough, this wonderful element is invisible. We open a window, and pure +air, rich in oxygen, comes in and takes the place of the bad air but we +cannot see the change. Water we see, but if the oxygen and the hydrogen +which compose the colourless liquid were separated, each would become at +once an invisible gas. The oxygen of solid rocks exists only in +combination with other elements. + +_Silicon_ is the element which, united with oxygen, makes the rock +called quartz. On the seashore the children are busy with their pails +and shovels digging in the white, clean sand. These grains are of +quartz,--fine crystals of a rock which forms nearly three-quarters of +the solid earth's substance. Not only in rocks, but out here in the +garden, the soil is full of particles of sand. You cannot get away from +it. + +_Aluminum_ is a light, bluish-white metal which we know best in +expensive cooking utensils. It is more abundant even than iron, but +processes of extracting it from the clay are still expensive. It is +oftenest found in combination with oxygen and silicon. While nearly +one-tenth of the earth's crust is composed of the metal aluminum, +four-fifths and more is composed of the minerals called silicates of +aluminum--oxygen, silicon, and aluminum in various combinations. It is +more plentiful than any other substance in rocks and in the clays and +ordinary soils, which are the finely ground particles of rock material. + +_Iron_ is one of the commonest of elements. We know it by its red +colour. A rusty nail is covered with oxide of iron, a combination which +is readily formed wherever iron is exposed to the action of water or +air. You have seen yellowish or red streaks in clefts of the rocks. This +shows where water has dissolved out the iron and formed the oxide. The +red colour of New Jersey soil is due to the iron it contains. Indeed, +the whole earth's crust is rich in iron which the water easily +dissolves. The roots of plants take up quantities of iron in solution +and this mounts to the blossoms, leaves, and fruit. The red or yellow +colour of autumn leaves, of apples, of strawberries, of tulips, and of +roses, is produced by iron. The rosy cheeks of children are due to iron +in the food they eat and in the water they drink. The doctor but follows +the suggestion of nature when he gives a pale and listless person a +tonic of iron to make his blood red. + +Iron is rarely found free, but it forms about five per cent. of the +crust of the earth, and it is believed to form at least one-fifth of the +unknown centre of the earth, the bulk of the globe, the weight of which +we know, but concerning the substance of which we can say little that is +positive. + +_Manganese_ is not a conspicuous element, but is found united with +oxygen in purplish or black streaks on the sides of rocks. It is +somewhat like iron, but much less common. + +_Calcium_ is the element that is the foundation of limestones. The +skeletons and shells of animals are made of calcite, a common mineral +formed by the uniting of carbon, oxygen, and calcium. Marbles are, +perhaps, the most permanent form of the limestone rocks. "Hard" water +has filtered through rocks containing calcite, and absorbed particles of +this mineral. From water thus impregnated, all animal life on the earth +obtains its bone-building and shell-building materials. + +_Carbon_ forms a large part of the tissues of plants and animals, and in +the remains of these it is chiefly found in the earth's crust. When +these burn or decay, the carbon remains as charcoal or escapes to the +air in union with oxygen as the well known carbonic acid gas. This is +one of the most important foods of plants. Joined with calcium it forms +the mineral calcite, or carbonate of lime. + +_Hydrogen_ is one of the two gases that unite to form water. Oxygen is +the other. Many kinds of rock contain a considerable amount of water. +Surface water sinks into porous soils and rocks, and accumulates in +pockets and veins which feed springs, and are the reserve water supply +that keeps our rivers flowing, even through dry weather. More water is +held by absorption in the earth's solid crust than in all the oceans and +seas and great lakes. + +Hydrogen, combined with carbon, occurs in solid rocks where the remains +of plants and animals have slowly decayed. From such processes the +so-called hydrocarbons, rock oil and natural gas, have accumulated. When +such decay goes on above ground, these valuable products escape into the +air. Marsh gas, whose feeble flame above decaying vegetation is the +will-o'-the-wisp of swamps, is an example. + +_Magnesium_, _potassium_, and _sodium_ are found in equal quantities in +the earth's crust, but never free. In union with chlorine, each forms a +soluble salt, and is thus found in water. Common salt, chloride of +sodium, is the most abundant of these. Water dissolves salt out of the +rocks, and carries it into the sea. Clouds that rise by the evaporation +of ocean water leave the salt behind, hence the seas are becoming more +and more salty, for the rivers carry salt to the oceans, which hold fast +all they get. + +_Phosphorus_ is an element found united with oxygen in the tissues of +both plants and animals. It is most abundant in bones. Rocks containing +fossil bones are rich in lime phosphates, which are important commercial +fertilizers for enriching the soil. Beds of these rocks are found and +mined in South Carolina and elsewhere. + +_Sulphur_ is well known as a yellow powder found most plentifully in +rocks that are near volcanoes. It is a needed element in plant and +animal bodies. It occurs in rocks, united with many different elements. +In union with oxygen and a metal it forms the group of minerals called +sulphates. In union with iron it forms sulphide of iron. The "fool's +gold" which Captain John Smith's colonists found in the sand at +Jamestown, was this worthless iron pyrites. + +_Chlorine_ is a greenish, yellow gas, very heavy, and dangerous to +inhale. If it gets into the lungs, it settles into the lowest levels, +and one must stand on one's head to get it out. As an element of the +earth's crust it is not very plentiful, but it is a part of all the +chlorides of sodium, magnesium, and potassium. In salt, it forms two per +cent. of the sea water. It is much less abundant in the rocks. + +To these elements we might add _nitrogen_, that invisible gas which +forms nearly four-fifths of our atmosphere, and is a most important +element of plant food in the soil. Most of the seventy elements are very +rare. Many are metals, like gold and iron and silver. Some are not +metals. Some are solid. A few are liquid, like the metal mercury, and +several are gaseous. Some are free and pure, and show no disposition to +unite with others. Nuggets of gold are examples of this. Some exist only +in union with other elements. This is the common rule among the +elements. Changes are constantly going on. The elements are constantly +abandoning old partnerships and forming new ones. Growth and decay of +plant and animal life are but parts of the great programme of constant +change which is going on and has been in progress since the world +began. + + + + +THE FIRST DRY LAND + + +When the earth's crust first formed it was still hot, though not so hot +as when it was a mass of melted, glowing substance. As it moved through +the cold spaces of the sky, it lost more heat and its crust became +thicker. At length the cloud masses became condensed enough to fall in +torrents of water, and a great sea covered all the land. This was before +any living thing, plant or animal, existed on our planet. Can you +imagine the continents and islands that form the land part of a map or +globe suddenly overwhelmed by the oceans, the names and boundaries of +which you have taken such pains to learn in the study of geography? The +globe would be one blank of blue water, and geography would be +abolished--and there would be nobody to study it. Possibly the fishes in +the sea might not notice any change in the course of their lives, except +when they swam among the ruins of buried cities and peered into the +windows of high buildings, or wondered what new kind of seaweed it was +when they came upon a submerged forest. + +In that old time of the great sea that covered the globe, we are told +that there was a dense atmosphere over the face of the deep. So things +were shaping themselves for the far-off time when life should exist, +not only in the sea, where the first life did appear, but on land. But +it took millions of years to fit the earth for living things. + +The cooling of the earth made it shrink, and the crust began to be +folded into gentle curves, as the skin of a shrunken apple becomes +wrinkled on the flesh. Some of these creases merely changed the depth of +water on the sea bottom; but one ridge was lifted above the water. The +water parted and streamed down its sloping sides, and a granite reef, +which shone in the sunshine, became the first dry land. It lay east and +west, and stretched for many miles. It is still dry land and is a part +of our own continent. Now it is but a small part of the country, but it +is known by geologists, who can tell its boundaries, though newer land +joins it on every side. It is named the Laurentian Hills, on geological +maps. Its southern border reaches along the northern boundary of the +Great Lakes to the head-waters of the Mississippi River. + +From this base, two ridges are lifted, forming a colossal V. One extends +northeast to Nova Scotia; the other northwest to the Arctic seas. The V +encloses Hudson Bay. + +Besides this first elongated island of bare rocks, land appeared in a +strip where now the Blue Ridge Mountains stretch from New England to +Georgia. The other side of the continent lifted up two folds of the +crust above sea level. They are the main ridges of the Colorado and the +Wasatch Mountains. Possibly the main ridge of the Sierra Nevada rose +also at this time. The Ozark group of mountains, too, showed as a few +island peaks above the sea. + +These first rocks were rapidly eaten away, for the atmosphere was not +like ours, but heavily charged with destructive gases, which did more, +we believe, to disintegrate the exposed rock surfaces than did the two +other forces, wind and water, combined. The sediment washed down to the +sea by rains, accumulated along the shores, filling the shallows and +thus adding to the width of the land areas. The ancient granite ridge of +the Laurentian Hills is now low, and slopes gently. This is true of all +very old mountains. The newer ones are high and steep. It takes time to +grind down the peaks and carry off the waste material loosened by +erosion. + +Far more material than could have been washed down the slopes of the +first land ridges came directly from the interior of the earth, and +spread out in vast, submarine layers upon the early crust. Volcanic +craters opened under water, and poured out liquid mineral matter, that +flowed over the sea bottom before it cooled. Imagine the commotion that +agitated the water as these submerged chimneys blew off their lids, and +discharged their fiery contents! It was long before the sea was cool +enough to be the home of living things. + +The layers of rock that formed under the sea during this period of the +earth's history are of enormous thickness. They were four or five miles +deep along the Laurentian Hills. They broadened the original granite +ridge by filling the sea bottom along the shores. The backbones of the +Appalachian system and the Cordilleras were built up in the same +way--the oldest rocks were worn away, and their debris built up newer +ones in strata. + +When these layers of rock became dry land, the earth's crust was much +more stable and cool than it had ever been before. The vast +rock-building of that era equals all that has been done since. The +layers of rocks formed since then do not equal the total thickness of +these first strata. So we believe that the time required to build those +Archaean rock foundations equals or surpasses the vast period that has +elapsed since the Archaean strata were formed. + +The northern part of North America has grown around those old granite +ridges by the gradual rising of the shores. The geologist may walk along +the Laurentian Hills, that parted the waters into a northern and a +southern ocean. He crosses the rocky beds deposited upon the granite; +then the successive beds formed as the land rose and the ocean receded. +Age after age is recorded in the rocks. Gradually the sea is crowded +back, and the land masses, east, west, and north, meet to form the +continent. Nowhere on the earth are the steps of continental growth +shown in unbroken sequence as they are in North America. + +How long ago did those first islands appear above the sea? Nobody +ventures a definite answer to this question. No one has the means of +knowing. But those who know most about it estimate that at the least one +hundred million years have passed since then--one hundred thousand +thousand years! + + + + +A STUDY OF GRANITE + + +In Every village cemetery it is easy to find shafts of gray or speckled +granite, the polished surfaces of which show that the granite is made of +small bits of different coloured minerals, cemented together into solid +rock. Outside the gate you will usually find a place where monuments and +gravestones may be bought. Here there is usually a stonecutter chipping +away on a block with his graving tools. He is a man worth knowing, and +because his work is rather monotonous he will probably be glad to talk +to a chance visitor and answer questions about the different kinds of +stone on which he works. + +There are bits of granite lying about on the ground. If you have a +hand-glass of low power, such as the botany class uses to examine the +parts of flowers, it will be interesting to look through it and see the +magnified surface of a flake of broken granite. Here are bits of glassy +quartz, clear and sparkling in the sun. Black and white may be all the +colours you make out in this specimen, or it may be that you see specks +of pink, dark green, gray, and smoky brown, all cemented together with +no spaces that are not filled. The particles of quartz are of various +colours, and are very hard. They scratch glass, and you cannot scratch +them with the steel point of your knife, as you can scratch the other +minerals associated with the grains of quartz. + +Granite is made of quartz, feldspar, and mica, sometimes with added +particles of hornblende. Feldspar particles have as wide a range of +colour as quartz, but it is easy to tell the two apart. A knife will +scratch feldspar, as it is not so hard as quartz. The crystals of +feldspar have smooth faces, while quartz breaks with a rough surface as +glass does. Feldspar loses its glassy lustre when exposed to the +weather, and becomes dull, with the soft lustre of pearl. + +Mica may be clear and glassy, and it ranges in colour from transparency +through various shades of brown to black. It has the peculiarity of +splitting into thin, leaf-like, flexible sheets, so it is easy to find +out which particles in a piece of granite are mica. One has only to use +one's pocket knife with a little care. Hornblende is a dark mineral +which contains considerable iron. It is found in lavas and granites, +where it easily decays by the rusting of the iron. It is not unusual to +see a rough granite boulder streaked with dark red rust from this cause. + +The crumbling of granite is constantly going on as a result of the +exposure of its four mineral elements to the air. Quartz is the most +stable and resistant to weathering. Soil water trickling over a granite +cliff has little effect on the quartz particles; but it dissolves out +some of the silicon. The bits of feldspar are even more resistant to +water than quartz is, but the air causes them to decay rapidly, and +finally to fall away in a sort of mealy clay. Mica, like feldspar, +decays easily. Its substance is dissolved by water and carried away to +become a kind of clay. The hornblende rusts away chiefly under the +influence of moist air and trickling water. + +We think of granite as a firm, imperishable kind of rock, and use it in +great buildings like churches and cathedrals that are to stand for +centuries. But the faces that are exposed to the air suffer, especially +in regions having a moist climate. The signs of decay are plainly +visible on the outer surfaces of these stones. Fortunate it is that the +weathering process cannot go very deep. + +The glassy polish on a smooth granite shaft is the silicon which acts as +a cement to bind all the particles together. It is resistant to the +weather. A polished shaft will last longer than an unpolished one. + +Granites differ in colouring because the minerals that compose them, the +feldspars, quartzes, micas, and hornblendes, have each so wide a range +of colour. Again, the proportions of the different mineral elements vary +greatly in different granites. A banded granite the colours of which +give it a stratified appearance is called a gneiss. + +We have spoken before of the seventy elements found in the earth's +crust. A mineral is a union of two or more of these different elements; +and we have found four minerals composing our granite rock. It may be +interesting to go back and inquire what elements compose these four +minerals. Quartz is made of silicon and oxygen. Feldspar is made of +silicon, oxygen, and aluminum. Mica is made of silicon, oxygen, and +carbon, with some mingling of potassium and iron and other elements in +differing proportions. Hornblende is made of silicon, oxygen, carbon, +and iron. + +The crumbling of a granite rock separates the minerals that compose it, +reducing some to the condition of clay, others to grains of sand. Some +of the elements let go their union and become free to form new unions. +Water and wind gather up the fragments of crumbling granite and carry +them away. The feldspar and mica fragments form clay; the quartz +fragments, sand. All of the sandstones and slates, the sand-banks and +sand beaches, are made out of crumbled granite, the rocky foundations of +the earth. + + + + +METAMORPHIC ROCKS + + +In the dawn of life on the earth, soft-bodied creatures, lowest in the +scale of being, inhabited the sea. The ancient volcanoes the +subterranean eruptions of which had spread layers of mineral substance +on the ocean floor, and heated the water to a high degree, had subsided. +The ocean was sufficiently cool to maintain life. The land was being +worn down, and its debris washed into the ocean. The first sand-banks +were accumulating along sandy shores. The finer sediment was carried +farther out and deposited as mud-banks. These were buried under later +deposits, and finally, by the rising of the earth's crust, they became +dry land. Time and pressure converted the sand-banks into sandstones; +the mud-banks into clay. The remains of living creatures utterly +disappeared, for they had no hard parts to be preserved as fossils. + +The shrinking of the earth's crust had crumpled into folds of the utmost +complexity those horizontal layers of lava rock poured out on the ocean +floor. Next, the same forces attacked the thick rock layers formed out +of sediment--the aqueous or water-formed sandstones and clays. + +The core of the globe contracts, and the force that crumples the crust +to fit the core generates heat. The alkaline water in the rocks joins +with the heat produced by the crumpling and crushing forces, acting +downward, and from the sides, to transform pure sandstone into glassy +quartzite, and clay into slate. In other words, water-formed rocks are +baked until they become fire-formed rocks. They are what the geologist +calls _metamorphic_, which means _changed_. + +In many mountainous regions there are breaks through the strata of +sandstone and slates and limestones, through which streams of lava have +poured forth from the heated interior. Along the sides of these fissures +the hot lava has changed all the rocks it touched. The heat of the +volcanic rock matter has melted the silica in the sand, which has +hardened again into a crystalline substance like glass. + +Have you ever visited a brick-yard? Here men are sifting clay dug out of +a pit or the side of a hill, adding sand from a sand-bank, and in a big +mixing box, stirring these two "dry ingredients" with water into a thick +paste. This dough is moulded into bricks, sun-dried, and then baked in +kilns themselves built of bricks. At the end of the baking, the soft, +doughy clay block is transformed into a hard, glassy, or dull brick. +From aqueous rock materials, fire has produced a metamorphic rock. +Volcanic action is imitated in this common, simple process of +brickmaking. + +Milwaukee brick is made of clay that has no iron in it. For this reason +the bricks are yellow after baking. Most bricks are red, on account of +the iron in the clay, which is converted into a red oxide, or rust, by +water and heat. + +Common flower pots and the tiles used in draining wet land are not +glazed, as hard-burned bricks are. The baking of these clay things is +done with much less heat. They are left somewhat porous. But the tiles +of roofs are baked harder, and get a surface glaze by the melting of the +glassy particles of the sand. + +As bricks vary in colour and quality according to the materials that +compose them, so the metamorphic rocks differ. The white sand one sees +on many beaches is largely quartz. This is the substance of pure, white +sandstone. Metamorphism melts the silica into a glassy liquid cement; +the particles are bound close together on cooling. The rock becomes a +white, granular quartzite, that looks like loaf sugar. If banded, it is +called gneiss. Such rocks take a fine polish. + +Pure limestone is also white and granular. When metamorphosed by heat, +it becomes white marble. The glassy cement that holds the particles of +lime carbonate shows as the glaze of the polished surface. It is silica. +One sees the same mineral on the face of polished granite. + +Clays are rarely pure. Kaolin is a white clay which, when baked, becomes +porcelain. China-ware is artificially metamorphosed kaolin. In the +early rocks the clay beds were transformed by heat into jasper and +slates. In beds where clay mingled with sand, in layers, gneiss was +formed. If mica is a prominent element, the metamorphic rock is easily +parted into overlapping, scaly layers. It is a mica schist. If +hornblende is the most abundant mineral, the same scaly structure shows +in a dark rock called hornblende schist, rich in iron. A schist +containing much magnesia is called serpentine. + +The bricks of the wall, the tiles on the roof, the flower pots on the +window sill, and the dishes on the breakfast table, are examples of +metamorphic rocks made by man's skill, by the use of fire and water +acting on sand and clay. Pottery has preserved the record of +civilization, from the making of the first crude utensils by cave men to +the finest expression of decorative art in glass and porcelain. + +The choicest material of the builder and the sculptor is limestone baked +by the fires under the earth's crust into marble. The most enduring of +all the rocks are the foundation granite, and the metamorphic rocks that +lie next to them. Over these lie thick layers of sedimentary rocks laid +down by water. In them the record of life on the earth is written in +fossils. + + + + +THE AIR IN MOTION + + +Most of the beautiful things that surround us and make our lives full of +happiness appeal to one or more of our five senses. The green trees we +can see, the bird songs we hear, the perfume of honey-laden flowers we +smell, the velvety smoothness of a peach we feel, and its rich pulp we +taste. But over all and through all the things we see and feel and hear +and taste and smell, is the life-giving air, that lies like a blanket, +miles in depth, upon the earth. The substance which makes the life of +plants and animals possible is, when motionless, an invisible, +tasteless, odourless substance, which makes no sound and is not +perceptible to the touch. + +Air fills the porous substance of the earth's crust for a considerable +distance, and even the water has so much air in it that fishes are able +to breathe without coming to the surface. It is not a simple element, +like gold, or carbon, or calcium, but is made up of several elements, +chief among which are nitrogen and oxygen. Four-fifths of its bulk is +nitrogen and one-fifth oxygen. There is present in air more or less of +watery vapour and of carbon dioxide, the gas which results from the +burning or decay of any substance. Although no more than one per cent. +of the air that surrounds us is water, yet this is a most important +element. It forms the clouds that bear water back from the ocean and +scatter it in rain upon the thirsty land. Solid matter in the form of +dust, and soot from chimneys, accumulates in the clouds and does a good +work in condensing the moisture and causing it to fall. + +It is believed that the air reaches to a height of one hundred to two +hundred miles above the earth's surface. If a globe six feet in diameter +were furnished with an atmosphere proportionately as deep as ours, it +would be about an inch in depth. At the level of the sea the air reaches +its greatest density. Two miles above sea-level it is only two-thirds as +dense. On the tops of high mountains, four or five miles above sea +level, the air is so rarefied as to cause the blood to start from the +nostrils and eyelids of explorers. The walls of the little blood-vessels +are broken by the expansion of the air that is inside. At the sea-level +air presses at the rate of fifteen pounds per square foot in all +directions. As one ascends to higher levels, the air pressure becomes +less and less. + +The barometer is the instrument by which the pressure of air is +measured. A glass tube, closed at one end, and filled with mercury, the +liquid metal often called quicksilver, is inverted in a cup of the same +metal, and so supported that the metal is free to flow between the two +vessels. The pressure of air on the surface of the mercury in the cup is +sufficient at the sea-level to sustain a column of mercury thirty +inches high in the tube. As the instrument is carried up the side of a +mountain the mercury falls in the tube. This is because the air pressure +decreases the higher up we go. If we should descend into the shaft of +the deepest mine that reaches below the sea level, the column of air +supported by the mercury in the cup would be a mile higher, and for this +reason its weight would be correspondingly greater. The mercury would +thus be forced higher in the tube than the thirty-inch mark, which +indicates sea-level. + +Another form of barometer often seen is a tube, the lower and open end +of which forms a U-shaped curve. In this open end the downward pressure +of the air rests upon the mercury and holds it up in the closed end, +forcing it higher as the instrument is carried to loftier altitudes. At +sea level a change of 900 feet in altitude makes a change of an inch in +the height of the mercury in the column. The glass tube is marked with +the fractions of inches, or of the metre if the metric system of +measurements is used. + +It is a peculiarity of air to become heated when it is compressed, and +cooled when it is allowed to expand again. It is also true that when the +sun rises, the atmosphere is warmed by its rays. This is why the hottest +part of the day is near noon when the sun's rays fall vertically. The +earth absorbs a great deal of the sun's heat in the daytime and through +the summer season. When it cools this heat is given off, thus warming +the surrounding atmosphere. In the polar regions, north and south, the +air is far below freezing point the year round. In the region of the +Equator it rarely falls below 90 degrees, a temperature which we find +very uncomfortable, especially when there is a good deal of moisture in +the air. + +If we climb a mountain in Mexico, we leave the sultry valley, where the +heat is almost unbearable, and very soon notice a change. For every +three hundred feet of altitude we gain there is a fall of one degree in +the temperature. Before we are half way up the slope we have left behind +the tropical vegetation, and come into a temperate zone, where the +plants are entirely different from those in the lower valley. As we +climb, the vegetation becomes stunted, and the thermometer drops still +lower. At last we come to the region of perpetual snow, where the +climate is like that of the frozen north. + +So we see that the air becomes gradually colder as we go north or south +from the Equator, and the same change is met as we rise higher and +higher from the level of the sea. + +It is only when air is in motion that we can feel and hear it, and there +are very few moments of the day, and days of the year, when there is not +a breeze. On a still day fanning sets the air in motion, and creates a +miniature breeze, the sound of which we hear in the swishing of the fan. +The great blanket of air that covers the earth is in a state of almost +constant disturbance, because of the lightness of warm air and the +heaviness of cold air. These two different bodies are constantly +changing places. For instance, the heated air at the Equator is +constantly being crowded upward by cold air which settles to the level +of the earth. Cold streams of air flow to the Tropics from north and +south of the Equator, and push upward the air heated by the sun. + +This constant inrush of air from north and south forms a double belt of +constant winds. If the earth stood still, no doubt the direction would +be due north and due south for these winds; but the earth rotates +rapidly from west to east upon its axis, carrying with it everything +that is securely fastened to the surface: the trees, the houses, etc. +But the air is not a part of the earth, not even so much as the seas, +the waters of which must stay in their proper basins, and be whirled +around with other fixed objects. The earth whirls so rapidly that the +winds from north and south of the Equator lag behind, and thus take a +constantly diagonal direction. Instead of due south the northern belt of +cold air drifts south-west and the southern belt drifts northwest. These +are called the Trade Winds. Near the Equator they are practically east +winds. + +The belt of trade winds is about fifty degrees wide. It swings northward +in our summer and southward in our winter, its centre following the +vertical position of the sun. Near the centre of the course which marks +the meeting of the northern with the southern winds is a "Belt of +Calms" where the air draws upward in a strong draught. The colder air of +the trade winds is pushing up the columns of light, heated air. This +strip is known by sailors as "the Doldrums," or "the region of +equatorial calms." Though never wider than two or three hundred miles, +this is a region dreaded by captains of sailing-vessels, for they often +lie becalmed for weeks in an effort to reach the friendly trade winds +that help them to their desired ports. Vessels becalmed are at the mercy +of sudden tempests which come suddenly like thunder-storms, and +sometimes do great damage to vessels because they take the sailors +unawares and allow no time to shorten sail. + +Until late years the routes of vessels were charted so that sailors +could take advantage of the trade winds in their long voyages. It was +necessary in the days of sailing-vessels for the captain to understand +the movements of winds which furnished the motive power that carried his +vessel. Fortunate it was for him that there were steady winds in the +temperate zones that he could take advantage of in latitudes north of +the Tropic of Cancer and south of the Tropic of Capricorn. What becomes +of the hot air that rises in a constant stream above the "Doldrums," +pushed up by the cooler trade winds that blow in from north and south? +Naturally this air cannot ascend very high, for it soon reaches an +altitude in which its heat is rapidly lost, and it would sink if it +were not constantly being pushed by the rising column of warm air under +it. So it turns and flows north and south at a level above the trade +winds. Not far north of the Tropic of Cancer it sinks to the level of +sea and land, and forms a belt of winds that blows ships in a +northeasterly direction. Between trades and anti-trades is another zone +of calms,--near the Tropics of Cancer and of Capricorn. + +The land masses of the continents with their high mountain ranges +interfere with these winds, especially in the northern hemisphere, but +in the Southern Pacific and on the opposite side of the globe the +"Roaring Forties," as these prevailing westerly winds are known by the +sailors, have an almost unbroken waste of seas over which they blow. In +the long voyages between England and Australia, and in the Indian trade, +the ships of England set their sails to catch the roaring forties both +going and coming. They accomplish this by sailing past the Cape of Good +Hope on the outward voyage and coming home by way of Cape Horn, thus +circling the globe with every trip. In the North Atlantic, traffic is +now mostly carried on in vessels driven by engines, not by sails. Yet +the westerly winds that blow from the West Indies diagonally across the +Atlantic are still useful to all sailing craft that are making for +British ports. + +From the north and from the south cold air flows down into the regions +of warmer climate. These polar winds are not so important to sea +commerce, but they do a great work in tempering the heat in the +equatorial regions. We cannot know how much our summers are tempered by +the cool breath of winds that blow over polar ice-fields. And the cold +regions of the earth, in their brief summer, enjoy the benefits of the +warm breezes that flow north and south from the heated equatorial +regions. + +The land, north and south, is made habitable by the clouds. They gather +their burdens of vapour from the warm seas, the wind drifts them north +and south, where they let it fall in rains that make and keep the earth +green and beautiful. From the clouds the earth gathers, like a great +sponge, the water that stores the springs and feeds rivers and lakes. +How necessary are the winds that transport the cloud masses! + +The air is the breath of life to all living things on our planet. Mars +is one of the sun's family so provided. Plants or animals could probably +live on the planet Mars. Do we think often enough of this invisible, +life-giving element upon which we depend so constantly? + +The open air which the wind purifies by keeping it in motion is the best +place in which to work, to play, and to sleep, when work and play are +done and we rest until another day comes. Indoors we need all the air we +can coax to come in through windows and doors. Fresh air purifies air +that is stale and unwholesome from being shut up. Nobody is afraid, +nowadays, to breathe night air! What a foolish notion it was that led +people to close their bedroom windows at night. Clean air, in plenty, +day and night, we need. Air and sunshine are the two best gifts of God. + + + + +THE WORK OF THE WIND + + +When the March wind comes blustering down the street, rudely dashing a +cloud of dust in our faces, we are uncomfortable and out of patience. We +duck our heads and cover our faces, but even then we are likely to get a +cinder in one eye, to swallow germs by the dozens, and to get a gray +coating of plain, harmless dust. We welcome the rain that lays the dust, +or its feeble imitation, the water sprinkler, that brings us temporary +relief. + +On the quietest day, even after a thorough sweeping and dusting of the +library, you are able to write your name plainly on the film of dust +that lies on the polished table. Take a book from the open shelves, and +blow into the trough of its top. This is always dusty. Where does the +dust come from? This is the house-keeper's riddle. + +The answer is not a hard one. I look out of my window on a street which +is famous as the road Washington took on his retreat from White Plains +to Trenton. It has always been the main thoroughfare between New York +and Philadelphia, and now is the route that automobiles follow. A +constant procession of vehicles passes my house, and to-day each one +approaches in a cloud of dust. The air is gray with suspended particles +of dirt. The wind carries the successive clouds, and they roll up +against the houses like breakers on the beach. Windows and doors are +loose enough to let dust sift in. When a door opens, the cloud enters +and lights on rugs and carpets and curtains. Any ledge collects its +share of dust. The beating of carpets and rugs disturbs the accumulated +dust of many months. + +[Illustration: In this lonely Arizona desert the wind drifts the sand +into dunes, just as it does on the toe of Cape Cod] + +[Illustration: The Grand Canyon of the Colorado shows on a magnificent +scale the work of water in cutting away rock walls] + +The wind sweeps the ploughed field, and takes all the dust it can carry. +It blows the finest top soil from our gardens into the street. It blows +soil from other fields and gardens into ours, so the level of our land +is not noticeably lowered. The wind strips the high land and drops its +burden on lower levels. This is one of the big jobs the water has to do, +and the wind is a valuable helper. To tear down the mountains and fill +in the valleys is the great work of the two partners, wind and water. + +Dead, still air holds the finest dust, without letting it fall. The +buoyancy of the particles overcomes their weight. We see them in a +sunbeam, like shining points of precious metal, and watch them. A light +breeze picks up bits of soil and litter, from the smallest up to a +certain size and weight. If the velocity of the wind increases, its +carrying power increases. It is able to carry bits that are larger and +heavier. The following table is exact and interesting: + + _Velocity_ _Pressure_ + _in Miles_ _in Pounds_ + _per Hour_ _per Sq. Ft._ + + Light breeze 14 1 + Strong breeze 42 9 + Strong gale 70 25 + Hurricane 84 36 + +The terrible paths of hurricanes are seen in forest countries. The trees +are uprooted, as if a great roller had crushed them, throwing the tops +all in one direction, and leaving the roots uncovered, and a sunken +pocket where each tree stood. On a steep, rocky slope, the uprooting of +scattered trees often loosens tons of rock, and sends the mass +thundering down the mountain-side. Much more destruction may be +accomplished by one brief tornado than by years of wear by ordinary +breezes. + +The wind does much to help the waves in their patient beating on rocky +shores. If the wind blows from the ocean and the tide is landward, the +two forces combine, and the loose rocks are thrown against the solid +beach with astonishing force. Even the gravel and the sharp sand are +tools of great usefulness to the waves in grinding down the resisting +shore. Up and back they are swept by the water, and going and coming +they have their chance to scratch or strike a blow. Boulders on the +beach become pockmarked by the constant sand-blast that plays upon them. +The lower windows of exposed seaside houses are dimmed by the sand that +picks away the smooth surface outside, making it ground glass by the +same process used in the factory. Lighthouses have this difficulty in +keeping their windows clear. The "lantern" itself is sometimes reached +by the sand grains. That is the cupola in which burns the great light +that warns vessels away from the rocks and tells the captain where he +is. + +In the Far Western States the telegraph poles and fence posts are soon +cut off at the ground by the flinty knives the wind carries. These are +the grains of sand that are blown along just above the ground. The trees +are killed by having their bark girdled in this way. The sand-storms +which in the orange and lemon region of California are called "Santa +Anas" sometimes last two or three days, and damage the trees by piercing +the tender bark with the needle-pointed sand. + +Wind-driven soil, gathered from the sides of bare hills and mountains, +fills many valleys of China with a fine, hard-packed material called +"loess." In some places it is hundreds of feet deep. The people dig into +the side of a hill of this loess and carry out the diggings, making +themselves homes, of many rooms, with windows, doors, and solid walls +and floors, all in one solid piece, like the chambered house a mole +makes underground in the middle of a field. So compact is the loess that +there is no danger of a cave-in. + +The hills of sand piled up on the southern shore of Lake Michigan, and +at Provincetown, at the toe of Cape Cod, are the work of the wind. On +almost any sandy shore these "dunes" are common. The long slope is +toward the beach that furnishes the sand. The wind does the building. Up +the slope it climbs, then drops its burden, which slides to the bottom +of an abrupt landward steep. There is a gradual movement inland if the +strongest winds come from the water. The shifting of the dunes threatens +to cover fertile land near them. In the desert regions, the border-land +is always in danger of being taken back again, even though it has been +reclaimed from the desert and cultivated for long years. + +Besides tearing down, carrying away, and building up again the fragments +of the earth's crust, the wind does much that makes the earth a pleasant +planet to live on. It drives the clouds over the land, bringing rains +and snows and scattering them where they will bless the thirsty ground +and feed the springs and brooks and rivers. It scatters the seeds of +plants, and thus plants forests and prairies and lovely mountain slopes, +making the wonderful wild gardens that men find when they first enter +and explore a new region. The trade winds blow the warm air of the +Tropics north and south, making the climate of the northern countries +milder than it would otherwise be. Sea winds blow coolness over the land +in summer, and cool lake breezes temper the inland regions. From the +snow-capped mountains come the winds that refresh the hot, tired worker +in the valleys. + +Everywhere the wind blows, the life-giving oxygen is carried. This is +what we mean when we speak of fresh air. Stagnant air is as unwholesome +as stagnant water. Constant moving purifies both. So we must give the +wind credit for some of the greatest blessings that come into our lives. +Light and warmth come from the sun. Pure water and pure air are gifts +the bountiful earth provides. Without them there would be no life on the +earth. + + + + +RAIN IN SUMMER + + + How beautiful is the rain! + After the dust and heat, + In the broad and fiery street, + In the narrow lane, + How beautiful is the rain! + + How it clatters along roofs, + Like the tramp of hoofs! + How it gushes and struggles out + From the throat of the overflowing spout! + Across the window-pane + + It pours and pours; + And swift and wide, + With a muddy tide, + Like a river down the gutter roars + The rain, the welcome rain! + + The sick man from his chamber looks + At the twisted brooks; + He can feel the cool + Breath of each little pool; + His fevered brain + Grows calm again, + And he breathes a blessing on the rain. + + --HENRY W. LONGFELLOW. + + + + +WHAT BECOMES OF THE RAIN? + + +The clouds that sail overhead are made of watery vapour. Sometimes they +look like great masses of cotton-wool against the intense blue of the +sky. Sometimes they are set like fleecy plumes high above the earth. +Sometimes they hang like a sullen blanket of gray smoke, so low they +almost touch the roofs of the houses. Indeed, they often rest on the +ground and then we walk through a dense fog. + +In their various forms, clouds are like wet sponges, and when they are +wrung dry they disappear--all their moisture falls upon the earth. When +the air is warm, the water comes in the form of rain. If it is cold, the +drops are frozen into hail, sleet, or snow. + +All of the water in the oceans, in the lakes and rivers, great and +small, all over the earth, comes from one source, the clouds. In the +course of a year enough rain and snow fall to cover the entire surface +of the globe to a depth of forty inches. This quantity of water amounts +to 34,480 barrels on every acre. What becomes of it all? + +We can easily understand that all the seas and the other bodies of water +would simply add forty inches to their depth, and many would become +larger, because the water would creep up on their gradually sloping +shores. We have to account for the rain and the snow that fall upon the +dry land and disappear. + +Go out after a drenching rainstorm and look for the answer to this +question. The gullies along the street are full of muddy, running water. +There are pools of standing water on level places, but on every slope +the water is hurrying away. The ground is so sticky that wagons on +country roads may mire to the hubs in the pasty earth. There is no use +in trying to work in the garden or to mow the lawn. The sod is soft as a +cushion, and the garden soil is water-soaked below the depth of a +spading-fork. + +The sun comes out, warm and bright, and the flagstones of the sidewalk +soon begin to steam like the wooden planks of the board walk. The sun is +changing the surface water into steam which rises into the sky to form a +part of another bank of clouds. The earth has soaked up quantities of +the water that fell. If we followed the racing currents in the gullies +we should find them pouring into sewer mains at various points, and from +these underground pipes the water is conducted to some outlet like a +river. All of the streams are swollen by the hundreds of brooks and +rivulets that are carrying the surface water to the lowest level. + +[Illustration: Rain and wind are the sculptors that have carved these +strange castles out of a rocky table] + +[Illustration: All the water in the seas, lakes, rivers, and springs +came out of the clouds] + +So we can see some of the rainfall going back to the sky, some running +off through rivulets to the sea, and some soaking into the ground. It +will be interesting to follow this last portion as it gradually settles +into the earth. The soil will hold a certain quantity, for it is made up +of fine particles, all separated by air spaces, and it acts like a +sponge. In seasons of drought and great heat the sun will draw this soil +water back to the surface, by forming cracks in the earth, and fine, +hair-like tubes, through which the vapour may easily rise. The gardener +has to rake the surface of the beds frequently to stop up these channels +by which the sun is stealing the precious moisture. + +The water that the surface soil cannot absorb sinks lower and lower into +the ground. It finds no trouble to settle through layers of sand, for +the particles do not fit closely together. It may come to a bed of clay +which is far closer. Here progress is retarded. The water may +accumulate, but finally it will get through, if the clay is not too +closely packed. Again it may sink rapidly through thick beds of gravel +or sand. Reaching another bed of clay which is stiffer by reason of the +weight of the earth above it, the water may find that it cannot soak +through. The only way to pass this clay barrier is to fill the basin, +and to trickle over the edge, unless a place is found in the bottom +where some looser substance offers a passage. Let us suppose that a +concave clay basin of considerable depth is filled with water-soaked +sand. At the very lowest point on the edge of this basin a stream will +slowly trickle out, and will continue to flow, as long as water from +above keeps the bowl full. + +It is not uncommon to find on hillsides, in many regions, little brooks +whose beginnings are traceable to springs that gush out of the ground. +The spring fills a little basin, the overflow of which is the brook. If +the source of this spring could be traced underground, we might easily +follow it along some loose rock formation until we come to a clay basin +like the one described above. We might have to go down quite a distance +and then up again to reach the level of this supply, but the level of +the water at the mouth of the spring can never be higher than the level +of the water in the underground supply basin. + +Often in hot summers springs "go dry." The level of water in the supply +basin has fallen below the level of the spring. We must wait until +rainfall has added to the depth of water in the basin before we can +expect any flow into the pool which marks the place where the brook +begins. + +Suppose we had no beds of clay, but only sand and gravel under the +surface soil. We should then expect the water to sink through this loose +material without hindrance, and, finding its way out of the ground, to +flow directly into the various branches of the main river system of our +region. After a long rain we should have the streams flooded for a few +days, then dry weather and the streams all low, many of them entirely +dry until the next rainstorm. + +Instead of this, the soil to a great depth is stored with water which +cannot get away, except by the slow process by which the springs draw +it off. This explains the steady flow of rivers. What should we do for +wells if it were not for the water basins that lie below the surface? A +shallow well may go dry. Its owner digs deeper, and strikes a lower +"vein" of water that gives a more generous supply. In the regions of the +country where the drift soil, left by the great ice-sheet, lies deepest, +the glacial boulder clay is very far down. The surface water, settling +from one level to another, finally reaches the bottom of the drift. +Wells have to be deep that reach this water bed. + +The water follows the slope of this bed and is drained into the ocean, +sometimes by subterranean channels, because the bed of the nearest river +is on a much higher level. So we must not think that the springs contain +only the water that feeds the rivers. They contain more. + +The layers of clay at different levels, from the surface down to the +bottom of the drift, form water basins and make it possible for people +to obtain a water supply without the expense of digging deep wells. The +clayey subsoil, only a few feet below the surface, checks the downward +course of the water, so that the sun can gradually draw it back, and +keep a supply where plant roots can get it. The vapour rising keeps the +air humid, and furnishes the dew that keeps all plant life comfortable +and happy even through the hot summer months. + +Under the drift lie layers of stratified rock, and under these are the +granites and other fire-formed rocks, the beginning of those rock masses +which form the solid bulk of the globe. We know little about the core of +the earth, but the granites that are exposed in mountain ridges are +found to have a great capacity for absorbing water, so it is not +unlikely that much surface water soaks into the rock foundations and is +never drained away into the sea. + +The water in our wells is often hard. It becomes so by passing through +strata of soil and rock made, in part, at least, of limestone, which is +readily dissolved by water which contains some acid. Soil water absorbs +acids from the decaying vegetation,--the dead leaves and roots of +plants. Rain water is soft, and so is the water in ponds that have muddy +basins, destitute of lime. Water in the springs and wells of the +Mid-Western States is "hard" because it percolates through limestone +material. In many parts of this country the well water is "soft," +because of the scarcity of limestone in the soil. + +I have seen springs around which the plants and the pebbles were coated +with an incrustation of lime. "Petrified moss" is the name given to the +plants thus turned to stone. The reason for this deposit is clear. +Underground water is often subjected to great pressure, and at this time +it is able to dissolve much more of any mineral substance than under +ordinary conditions. When the pressure is released, the water is unable +to hold in solution the quantity of mineral it contains; therefore, as +it flows out through the mouth of the spring, the burden of mineral is +laid down. The plants coated with the lime gradually decay, but their +forms are preserved. + +There are springs the water of which comes out burdened with iron, which +is deposited as a yellowish or red mineral on objects over which it +flows. Ponds fed by these springs accumulate deposits of the mineral in +the muddy bottoms. Some of the most valuable deposits of iron ore have +accumulated in bogs fed by iron-impregnated spring water. In a similar +way lime deposits called marl or chalk are made. + + + + +THE SOIL IN FIELDS AND GARDENS + + +City and country teachers are expected to teach classes about the +formation and cultivation of soil. It is surprising how much of the +needed materials can be brought in by the children, even in the cities. +The beginning is a flowering plant growing in a pot. A window box is a +small garden. A garden plot is a miniature farm. + +_Materials to collect for study indoors._ A few pieces of different +kinds of rock: Granite, sandstone, slate; gravelly fragments of each, +and finer sand. Pebbles from brooks and seashore. Samples of clays of +different colors, and sands. Samples of sandy and clay soils, black pond +muck, peat and coal. Rock fossils. A box of moist earth with earthworms +in it. _Keep it moist._ A piece of sod, and a red clover plant with the +soil clinging to its roots. + +_What is soil?_ It is the surface layer of the earth's crust, sometimes +too shallow on the rocks to plough, sometimes much deeper. Under deep +soil lies the "subsoil," usually hard and rarely ploughed. + +_What is soil made of?_ Ground rock materials and decayed remains of +animal and plant life. By slow decay the soil becomes rich food for the +growing of new plants. Wild land grows up to weeds and finally to +forests. The soil in fields and gardens is cultivated to make it +fertile. Plants take fertility from the soil. To maintain the same +richness, plant food must be put back into the soil. This is done by +deep tillage, and by mixing in with the soil manures, green crops, like +clover, and commercial fertilizers. + +_Plants must be made comfortable, and must be fed._ Few plants are +comfortable in sand. It gets hot, it lets water through, and it shifts +in wind and is a poor anchor for roots. Clay is so stiff that water +cannot easily permeate it; roots have the same trouble to penetrate it +and get at the food it is rich in. Air cannot get in. + +Sand mixed with clay makes a mellow soil, which lets water and air pass +freely through. The roots are more comfortable, and the tiny root hairs +can reach the particles of both kinds of mineral food. But the needful +third element is decaying plant and animal substances, called "humus." +These enrich the soil, but they do a more important thing: their decay +hastens the release of plant food from the earthy part of the soil, and +they add to it a sticky element which has a wonderful power to attract +and hold the water that soaks into the earth. + +_What is the best garden soil?_ A mixture of sand, clay, and humus is +called "loam." If sand predominates, it is a sandy loam--warm, mellow +soil. If clay predominates, we have a clay loam--a heavy, rich, but +cool soil. All gradations between the two extremes are suited to the +needs of crops, from the melons on sandy soil, to celery that prefers +deep, cool soil, and cranberries that demand muck--just old humus. + +_How do plant roots feed in soil?_ By means of delicate root hairs which +come into contact with particles of soil around which a film of soil +water clings. This fluid dissolves the food, and the root absorbs the +fluid. Plants can take no food in solid form. Hence it is of the +greatest importance to have the soil pulverized and spongy, able to +absorb and hold the greatest amount of water. The moisture-coated soil +particles must have air-spaces between them. Air is as necessary to the +roots as to the tops of growing plants. + +_Why does the farmer plough and harrow and roll the land?_ To pulverize +the soil; to mellow and lighten it; to mix in thoroughly the manure he +has spread on it, and to reach, if he can, the deeper layers that have +plant food which the roots of his crops have not yet touched. Killing +weeds is but a minor business, compared with tillage. + +Later, ploughing or cultivating the surface lightly not only destroys +the weeds, but it checks the loss of water by evaporation from the +cracks that form in dry weather. Raking the garden once a day in dry +weather does more good than watering it. The "dust mulch" acts as a cool +sunguard over the roots. + +_The process of soil-making._ If the man chopping wood in the Yosemite +Valley looks about him he can see the soil-making forces at work on a +grand scale. The bald, steep front of El Capitan is of the hardest +granite, but it is slowly crumbling, and its fragments are accumulating +at the bottom of the long slope. Rain and snow fill all crevices in the +rocks. Frost is a wonderful force in widening these cracks, for water +expands when it freezes. The loosened rock masses plough their way down +the steep, gathering, as they go, increasing power to tear away any +rocks in their path. + +Wind blows finer rock fragments along, and they lodge in cracks. Fine +dust and the seeds of plants are lodged there. The rocky slopes of the +Yosemite Valley are all more or less covered with trees and shrubs that +have come from wind-sown seeds. These plants thrust their roots deeper +each year into the rock crevices. The feeding tips of roots secrete +acids that eat away lime and other substances that occur in rocks. Dead +leaves and other discarded portions of the trees rot about their roots, +and form soil of increasing depth. The largest trees grow on the rocky +soil deposited at the base of the slope. The tree's roots prevent the +river from carrying it off. + +When granite crumbles, its different mineral elements are separated. +Clear, glassy particles of quartz we call sand. Dark particles of +feldspar become clay, and may harden into slate. Sand may become +sandstone. Exposed slate and sandstone are crumbled by exposure to wind +and frost and moving water, and are deposited again as sand-bars and +beds of clay. + +The most interesting phase of soil study is the discovery of what a work +the humble earthworm does in mellowing and enriching the soil. + + + + +THE WORK OF EARTHWORMS + + +The farmer and the gardener should expect very poor crops if they +planted seed without first ploughing or spading the soil. Next, its fine +particles must be separated by the breaking of the hard clods. A wise +man ploughs heavy soil in the fall. It is caked into great clods which +crumble before planting time. The water in the clods freezes in winter. +The expansion due to freezing makes this soil water a force that +separates the fine particles. So the frost works for the farmer. + +Just under the surface of the soil lives a host of workers which are our +patient friends. They work for their living, and are perhaps unconscious +of the fact that they are constantly increasing the fertility of the +soil. They are the earthworms, also called fishworms, which are +distributed all over the world. They are not generally known to farmers +and gardeners as friendly, useful creatures, and their services are +rarely noticed. We see robins pulling them out of the ground, and we are +likely to think the birds are ridding us of a garden pest. What we need +is to use our eyes, and to read the wonderful discoveries recorded in a +book called "Vegetable Mould and Earthworms," written by Charles +Darwin. + +The benefits of ploughing and spading are the loosening and pulverizing +of the packed earth; the mixing of dead leaves and other vegetation on +and near the surface with the more solid earth farther down; the letting +in of water and air; and the checking of loss of water through cracks +the sun forms by baking the soil dry. + +The earthworm is a creature of the dark. It cannot see, but it is +sufficiently sensitive to light to avoid the sun, the rays of which +would shrivel up its moist skin. Having no lungs or gills, the worm uses +the skin as the breathing organ; and it must be kept moist in order to +serve its important use. This is why earthworms are never seen above +ground except on rainy days, and never in the top soil if it has become +dry. In seasons of little rain, they go down where the earth is moist, +and venture to the surface only at night, when dew makes their coming up +possible. + +Earthworms have no teeth, but they have a long snout that protrudes +beyond the mouth. Their food is found on and in the surface soil. They +will eat scraps of meat by sucking the juices, and scrape off the pulp +of leaves and root vegetables in much the same way. Much of their +subsistence is upon organic matter that can be extracted from the soil. +Quantities of earth are swallowed. It is rare that an earthworm is dug +up that does not show earth pellets somewhere on their way through the +long digestive canal. The rich juices of plant substance are absorbed +from these pellets as they pass through the body. + +Earthworms explore the surface of the soil by night, and pick up what +they can find of fresh food. Nowhere have I heard of them as a nuisance +in gardens, but they eagerly feed on bits of meat, especially fat, and +on fresh leaves. They drag all such victuals into their burrows, and +begin the digestion of the food by pouring on it from their mouths a +secretion somewhat like pancreatic juice. + +The worms honeycomb the earth with their burrows, which are long, +winding tubes. In dry or cold weather these burrows may reach eight feet +under ground. They run obliquely, as a rule, from the surface, and are +lined with a layer of the smooth soil, like soft paste, cast from the +body. The lining being spread, the burrow fits the worm's body closely. +This enables it to pass quickly from one end to the other, though it +must wriggle backward or forward without turning around. + +At the lower end of the burrow, an enlarged chamber is found, where +hibernating worms coil and sleep together in winter. At the top, a +lining of dead leaves extends downward for a few inches, and in day time +a plug of the same material is the outside door. At night the worm comes +to the surface, and casts out the pellets of earth swallowed. The burrow +grows in length by the amount of earth scraped off by the long snout +and swallowed. The daily amount of excavation done is fairly estimated +by the castings observed each morning on the surface. + +One earthworm's work for the farmer is not very much, but consider how +many are at work, and what each one is doing. It is boring holes through +the solid earth, and letting in the surface water and the air. It is +carrying the lower soil up to the surface, often the stubborn subsoil, +that no plough could reach. It is burying and thus hastening the decay +of plant fibre, which lightens heavy soil and makes it rich because it +is porous. Moreover, the earthworms are doing over and over again this +work of fining and turning over the soil, which the plough does but +seldom. + +By the continuous carrying up of their castings, the earthworms +gradually bury manures spread on the surface. The collapse of their +burrows and the making of new ones keep the soil constantly in motion. +The particles are being loosened and brought into contact with the soil +water, that dissolves, and thus frees for the use of feeding roots, the +plant food stored in the rock particles that compose the mineral part of +the soil. + +The weight of earth brought to the surface by worms in the course of a +year has been carefully estimated. Darwin gives seven to eighteen tons +per acre as the lowest and highest reports, based on careful collecting +of castings by four observers, working on small areas of totally +different soils. In England, earthworms have done a great deal more +toward burying boulders and ancient ruins than any other agency. They +eagerly burrow under heavy objects, the weight of which causes them to +crush the honeycombed earth. Undiscouraged, the earthworms repeat their +work. + +"Long before man existed, the land was regularly ploughed, and continues +still to be ploughed by earthworms. It may be doubted whether there are +many other animals which have played so important a part in the history +of the world as have these lowly organized creatures." + +After years of study, Charles Darwin came to this conclusion. The more +we study the lives of these earth-consuming creatures, the more fully do +we believe what the great nature student said. The fertile soil is made +of rock meal and decayed leaves and roots. Only recently have ploughs +been invented. But the great forest crops have grown in soil made mellow +by the earthworm's ploughing. + + + + +QUIET FORCES THAT DESTROY ROCKS + + +Wind and water are the blustering active agents we see at work tearing +down rocks and carrying away their particles. They do the most of this +work of levelling the land; but there are quiet forces at work which +might not attract our attention at all, and yet, without their help, +wind and running water would not accomplish half the work for which they +take the credit. + +The air contains certain destructive gases which by their chemical +action separate the particles of the hardest rocks, causing them to +crumble. Now the wind blows away these crumbling particles, and the +solid unchanged rock beneath is again exposed to the crumbling agencies. + +The changes in temperature between day and night cause rocks to contract +and expand, and these changes put a strain upon the mineral particles +that compose them. Much scaling of rock surfaces is due to these causes. +Building a fire on top of a rock, and then dashing water upon the heated +mass, shatters it in many directions. This process merely intensifies +the effect produced by the mild changes of winter and summer. Water is +present in most rocks, in surprising quantities, often filling the +spaces in porous rocks like sandstones. + +When winter brings the temperature down to the freezing point, the water +near the surface of the rock first feels it. Ice forms, and every +particle of water is swollen by the change. A strain is put upon the +mineral particles against which the particles of ice crowd for more +room. Frost is a very powerful agent in the crumbling of rocks, as well +as of stubborn clods of earth. In warm climates, and in desert regions +where there is little moisture in the rocks, this destructive action of +freezing water is not known. In cold countries, and in high altitudes, +where the air is heavy with moisture, its greatest work is done. + +Some kinds of rock decay when they become dry, and resist crumbling +better when they absorb a certain amount of moisture. Alternate wetting +and drying is destructive to certain rocks. + +One of the unnoticed agents of rock decay is the action of lowly plants. +Mosses grow upon the faces of rocks, thrusting their tiny root processes +into pits they dig deeper by means of acids secreted by the delicate +tips. You have seen shaded green patches of lichens, like little rugs, +of different shapes, spread on the surface of rocks. But you cannot see +so well the work these growths are doing in etching away the surface, +and feeding upon the decaying mineral substance. + +Mosses and lichens do a mighty work, with the help of water, in +reducing rocks to their original elements, and thus forming soil. No +plants but lichens and mosses can grow on the bare faces of rocks. As +their root-like processes lengthen and go deeper into the rock face, +particles are pried off, and the under-substance is attacked. Higher +plants then find a footing. Have you not seen little trees growing on a +patch of moss which gets its food from the air and the rock to which it +clings? The spongy moss cushion soaks up the rain and holds it against +the rock face. A streak of iron in the rock may cause the water to +follow and rust it out, leaving a distinct crevice. Now the roots of any +plant that happens to be growing on the moss may find a foot-hold in the +crack. Streaks of lime in a rock readily absorb water, which gradually +dissolves and absorbs its particles, inviting the roots to enter these +new passages and feed upon the disintegrating minerals. Dead leaves +decay, and the acids the trickling water absorbs from them are +especially active in disintegrating lime rocks. + +From such small beginnings has resulted the shattering of great rock +masses by the growth of plants upon them. Tree roots that grow in rock +crevices exert a power that is irresistible. The roots of smaller plants +do the same great work in a quieter way. + +When a hurricane or a flood tears down the mountain-side, sweeping +everything before it, trees, torn out by the roots, drag great masses +of rock and soil into the air, and fling them down the slope. Wind and +water thus finish the destruction which the humble mosses and lichens +began. What seemed an impregnable fortress of granite has crumbled into +fragments. Its particles are reduced to dust, or are on the way to this +condition. The plant food locked up in granite boulders becomes +available to hungry roots. Forests, grain-fields, and meadows cover the +work of destructive agencies with a mantle of green. + + + + +HOW ROCKS ARE MADE + + +The granite shaft is made out of the original substance of the earth's +crust. Its minerals are the elements out of which all of the rock masses +of the earth are formed, no matter how different they look from granite. +Sandstone is made of particles of quartz. Clay and slate are made out of +feldspar and mica. Iron ore comes from the hornblende in granite. The +mineral particles, reassembled in different proportions, form all of the +different rocks that are known. + +Here in my hand is a piece of pudding-stone. It is made of pebbles of +different sizes, each made of different coloured minerals. The pebbles +are cemented together with a paste that has hardened into stone. This +kind of rock the geologists call _conglomerate_. Pudding-stone is the +common name, for the pebbles in the pasty matrix certainly do suggest +the currants and the raisins that are sprinkled through a Christmas +pudding. + +Under the seashores there are forming to-day thick beds of sand. The +rivers bring the rock material down from the hills, and it is sorted and +laid down. The moving water drops the heaviest particles near shore, and +carries the finer ones farther out before letting them fall. + +[Illustration: The town of Cripple Creek, Colorado, which has grown up +like magic since 1891, covers the richest gold and silver mines in the +world] + +[Illustration: The level valley is filled up with fine rock flour washed +from the sides of the neighboring mountains] + +The hard water, that comes through limestone rocks, adds lime in +solution to the ocean water. All the shellfish of the sea, and the +creatures with bony skeletons, take in the bone-building, shell-making +lime with their food. Generations of these inhabitants of the sea have +died, and their shells and bones have accumulated and been transformed +into thick beds of limestone on the ocean floor. This is going on +to-day; but the limestone does not accumulate as rapidly as when the +ocean teemed with shell-bearing creatures of gigantic size. Of these we +shall speak in another chapter. + +The fine dust that is blown into the ocean from the land, and that makes +river water muddy, accumulates on the sea bottom as banks of mud, which +by the burden of later deposits is converted into clay. Sandstone is but +the compressed sand-bank. + +In the study of mountains, geologists have discovered that old seashores +were thrown up into the first great ridges that form the backbone of a +mountain system. The Rocky Mountains, and the Appalachian system on the +east, were made out of thick strata of rocks that had been formed by +accumulations of mud and sand--the washings of the land--on the opposite +shores of a great mid-continental sea, that stretched from the crest of +one great mountain system across to the other, and north and south from +the Laurentian Hills to the Gulf of Mexico. The great weight of the +accumulating layers of rock materials on one side, and the wasted land +surfaces on the other, made the sea border a line of greatest weakness +in the crust of the earth. The shrinking of the globe underneath caused +the break; mashing and folding followed, throwing the ridge above +sea-level, and making dry land out of rock waste which had been +accumulating, perhaps for millions of years, under the sea. The +wrinkling of the earth's crust was the result of crushing forces which +produced tremendous heat. + +Streams of lava sprang out through the fissures and poured streams of +melted rock down the sides of the fold, quite burying, in many places, +the layers of limestone, sandstone, and clay. Between the strata of +water-formed rocks there were often created chimney-like openings, into +which molten rock from below was forced, forming, when cool, veins and +dikes of rock material, specimens of the substance of the earth's +interior. + +Tremendous pressure and heat, acting upon stratified rocks saturated +with water transform them into very different kinds of rock. Limestone, +subjected to these forces, is changed into marble. Clays are transformed +into slates. Sandstone is changed into quartzite, the sand grains being +melted so as to become no longer visible to the naked eye. The +anthracite coal of the Pennsylvania mountains is the result of heat and +pressure acting upon soft coal. Associated with these beds of hard coal +are beds of black lead, or graphite, the substance used in making "lead" +pencils. We believe that the same forces that operated to transform clay +rocks into slate, and limestone into marble, transformed soft coal into +hard, and hard coal into graphite, in the days when the earth was young. + +The word _sedimentary_ is applied to rocks which were originally laid +down under water, as sediment, brought by running water, or by wind, or +by the decay of organic substances. _Stratified_ rocks are those which +are arranged in layers. Sedimentary rocks will fall into this class. +_Aqueous_ rocks are those which are formed under water. Most of the +stratified and sedimentary rocks, but not all, may be included under +this term. Rocks that are made out of fragments of other rocks torn down +by the agencies of erosion are called _fragmental_. Wind, water, and ice +are the three great agencies that wear away the land, bring rock +fragments long distances, and deposit them where aqueous rocks are being +formed. Volcanic eruptions bring material from the earth's interior. +This material ranges all the way from huge boulders to the finest +impalpable dust, called volcanic ashes. Rivers of ice called glaciers +crowd against their banks, loosening rock masses and carrying away +fragments of all sizes, in their progress down the valley. Brooks and +rivers carry the pebbles and the larger rock masses they are able to +loosen from their walls and beds, and grind them smooth as they move +along toward lower levels. + +The air itself causes rocks to crumble; percolating water robs them of +their soluble salts, reducing even solid granite to a loose mass of +quartz grains and clay. Plants and animals absorb as food the mineral +substances of rocks, when they are dissolved in water. They transform +these food elements into their own body substance, and finally give back +their dead bodies, the mineral substances of which are freed by decay to +return to the earth, and become elements of rock again. + +The decay of rock is well shown by the materials that accumulate at the +base of a cliff. Angular fragments of all sizes, but all more or less +flattened, come from strata of shaly rock, that can be seen jutting out +far above. A great deal of this sort of material is found mingled with +the soil of the Northeastern States. Round pebbles in pudding-stone have +been formed in brook beds and deposited on beaches where they have +become caked in mud and finally consolidated into rock. If the beach +chanced to be sandy instead of muddy, a matrix of sandy paste holds the +larger pebbles in place. Limestone paste cements together the pebbles of +limestone conglomerates. + +In St. Augustine many of the houses are built of coquina rock, a mass of +broken shells which have become cemented together by lime mud, derived +from their own decay. On the slopes of volcanoes, rock fragments of all +kinds are cemented together by the flowing lava. So we see that there +are pudding-stones of many kinds to be found. If some solvent acid is +present in the water that percolates through these rocks it may soften +the cement and thus free the pebbles, reducing the conglomerate again to +a mere heap of shell fragments, or gravel, or rounded pebbles. + +The story of rock formation tells how fire and water, and the two +combined, have made, and made over, again and again, the substance of +the earth's crust. Chemical and physical changes constantly tear down +some portions of the earth to build up others. The constant, combined +effort of wind and water is to level the earth and fill up the ocean +bed. Rocks are constantly being formed; the changes that have been going +on since the world began are still in progress. We can see them all +about us on any and every day of our lives. + + + + +GETTING ACQUAINTED WITH A RIVER + + +I have two friends whose childhood was spent in a home on the banks of a +noble eastern river. Their father taught the boy and the girl to row a +boat, and later each learned the more difficult art of managing a canoe. +On holidays they enjoyed no pleasure so much as a picnic on the +river-bank at some point that could be reached by rowing. As they grew +older, longer trips were planned, and the river was explored as far as +it was navigable by boat or canoe. Last summer when vacation came, these +two carried out a long-cherished plan to find the beginning of the +river--to follow it to its source. So they left home, and canoed +up-stream, until the stream became a brook, so shallow they could go no +farther. Then they followed it on foot--wading, climbing, making little +detours, but never losing the little river. At last they came to the +beginning of it--a tiny rivulet trickled out of the side of a hill, +filling a wooden keg that formed a basin, where thirsty passers-by could +stoop and drink. They decided to mark the spring, so that people who +found it later, and were refreshed by its clear water, might know that +here was born the greatest river of a great state. But they were not the +original discoverers. Above the spring, a board was nailed to a tree, +saying that this is the headwater of the river with the beautiful Indian +name, Susquehanna. + +It was a dry summer, and the overflow of the basin was almost all drunk +up by the thirsty ground. They could scarcely follow it, except by the +groove cut by the rivulet in seasons when the flow was greater. They +followed the runaway brook, through the grass roots, that almost hid it. +As the ground grew steeper, it hurried faster. Soon it gathered the +water of other springs, which hurried toward it in small rivulets, +because its level was lower. Water always seeks the lowest level it can +find. Sometimes marshy spots were reached where water stood in the holes +made by the feet of cattle that came there to drink. The water was +muddy, and seemed to stand still. But it was settling steadily, and at +one side the little river was found, flowing away with the water it drew +from the swampy, springy ground. All the mud was gone, now; the water +was clear. It flowed in a bed with a stony floor, and there were rough +steps where the water fell down in little sheets, forming a waterfall, +the first of many that make this river beautiful in the upper half of +its course. To get from the high level of that hillside spring to the +low level of the sea, the water has to make a fall of twenty-three +hundred feet, but it makes the descent gradually. It could not climb +over anything, but always found a way to get around the rocks and hills +that stood in its way. When the flat marsh land interfered, the water +poured in and overflowed the basin at the lowest margin. + +In the rocky ground the two explorers found that the stream had widened +its channel by entering a narrow crevice and wearing away its walls. The +continual washing of the water wears away stone. Rocks are softened by +being wet. Streaks of iron in the hardest granite will rust out and let +the water in. Then the lime in rocks is easily dissolved. Every dead +leaf the river carried along added an acid to the water, and this made +easier the process of dissolving the limestone. + +Every crumbling rock gives the river tools that it uses like hammer and +chisel and sandpaper to smooth all the uneven surfaces in its bed, to +move stumbling blocks, and to dig the bed deeper and wider. The steeper +the slope is, the faster the stream flows, and the larger the rocks it +can carry. Rocks loosened from the stream bed are rolled along by the +current. Then bang! against the rocks that are not loose, and often they +are able to break them loose. The fine sand is swept along, and its +sharp points strike like steel needles, and do a great work in polishing +roughness and loosening small particles from the stream bed. The bigger +pebbles of the stream have banged against the rock walls, with the same +effect, smoothing away unevenness and pounding fragments loose, rolling +against one another, and getting their own rough corners worn away. + +The makers of stone marbles learned their business from a brook. They +cut the stone into cubical blocks, and throw them into troughs, into +which is poured a stream of running water. The blocks are kept in +motion, and the grinding makes each block help the rest to grind off the +eight corners and the twelve ridges of each one. The water becomes muddy +with the fine particles, just as the drip from a grindstone becomes +unclean when an axe is ground. Pretty soon all the blocks in the trough +are changed into globes--the marbles that children buy at the shops when +marble season comes around. + +I suppose if the troughs are not watched and emptied in time, the +marbles would gradually be ground down to the size of peas, then to the +size of small bird shot, and finally they would escape as muddy water +and fine sand grains. + +Sure it is that the sandy shores that line most rivers are the remnants +of hard rocks that have been torn out and ground up by the action of the +current. + +Not very many miles from its first waterfall the stream had grown so +large that my two friends knew that they would soon find their canoes. +The plan now was to float down the curious, winding river and to learn, +if the river and the banks could tell them, just why the course was so +crooked on the map. They came into a broad, level valley where streams +met them, coming out of deep clefts between the hills they were leaving +behind them. The banks were pebbly, but blackened with slimy mud that +made the water murky. The current swerved from one side to the other, +sometimes quite close to the bank, where the river turned and formed a +deep bend. On this side the bank was steep, the roots of plants and +trees exposed. On the opposite side a muddy bank sloped gently out into +the stream. Here building up was going on, to offset the tearing down. + +The sharp bends are made sharper, once the current is deflected from the +middle of the stream to one side. At length the loops bend on each other +and come so near together that the current breaks through, leaving a +semicircular bayou of still water, and the river's course straightened +at that place. It must have been in a spring flood that this cut-off was +made, and, the break once made was easily widened, for the soil is fine +mud which, when soaked, crumbles and dissolves into muddy water. + +Stately and slow that river moves down to the bay, into which it empties +its load. The rain that falls on hundreds of square miles of territory +flows into the streams that feed this trunk. The little spring that is +the headwater of the system is but one of many pockets in the hillsides +that hold the water that soaks into the ground and give it out by slow +degrees. Surface water after a rain flows quickly into the streams. It +is the springs that hold back their supply and keep the rivers from +running dry in hot weather. + +Do they feel now that they know their river? Are they ready to leave it, +and explore some other? Indeed, no. They are barely introduced to it. +All kinds of rivers are shown by the different parts of this one. It is +a river of the mountains and of the lowland. It flows through woods and +prairies, through rocky passes and reedy flats. It races impetuously in +its youth, and plods sedately in later life. The trees and the other +plants that shadow this stream, and live by its bounty, are very +different in the upland and in the lowland. The scenery along this +stream shows endless variety. Up yonder all is wild. Down here great +bridges span the flood, boats of all kinds carry on the commerce between +two neighbour cities. A great park comes down to the river-bank on one +side. Canoes are thick as they can paddle on late summer afternoons. + +No one can ever really know a river well enough to feel that it is an +old story. There is always something new it has to tell its friends. So +my two explorers say, and they know far more about their friendly river +than I do. + + + + +THE WAYS OF RIVERS + + +A canal is an artificial river, built to carry boats from one place to +another. Its course is, as nearly as possible, a straight line between +two points. A river, we all agree, is more beautiful than a canal, for +it winds in graceful curves, in and out among the hills, its waters +seeking the lowest level, always. + +No artist could lay out curves more beautiful than the river forms. +These curves change from year to year, some slowly, some more rapidly. +It is not hard to understand just why these changes take place. + +Some rivers are dangerous for boating at certain points. The current is +strong, and there are eddies and whirlpools that have to be avoided, or +the boat becomes unmanageable. People are drowned each season by +trusting themselves to rivers the dangerous tricks of which they do not +know. Deep holes are washed out of the bed of the stream by whirling +eddies. The pot-holes of which people talk are deep, rounded cavities, +ground out of the rocky stream-bed by the scouring of sand and loose +stones driven by whirling eddies in shallow basins. Every year deepens +each pot-hole until some change in the stream-bed shifts the eddy to +another place. + +No stream finds its channel ready-made; it makes its own, and constantly +changes it. The current swings to one side of the channel, lifting the +loose sediment and grinding deeper the bed of the stream. The water lags +on the opposite side, and sediment falls to the bottom. So the +building-up of one side is going on at the same time that the +tearing-down process is being carried on on the other. With the lowering +of the bed the river swerves toward one bank, and a hollow is worn by +slow degrees. The current swings into this hollow, and in passing out is +thrown across the stream to the opposite bank. Here its force wears away +another hollow; and so it zigzags down-stream. The deeper the hollows, +the more curved becomes the course, if the general fall is but moderate. +It is toward the lower courses of the stream that the winding becomes +more noticeable. The sediment that is carried is deposited at the point +where the current is least strong, so that while the outcurves become +sharper by the tearing away of the stream's bank, the incurves become +sharper by the building up of this bank. + +The Mississippi below Memphis is thrown into a wonderful series of +curves by the erosion and the deposit caused by the current zigzagging +back and forth from one bank to the other. Gradually the curves become +loops. The river's current finally jumps across the meeting of the +curves, and abandons the circular bend. It becomes a bayou or lagoon of +still water, while the current flows on in the straightened channel. +All rivers that flow through flat, swampy land show these intricate +winding channels and many lagoons that have once been curves of the +river. + +No one would ever mistake a river for a lake or any other body of water, +yet rivers differ greatly in character. One tears its way along down its +steep, rock-encumbered channel between walls that rise as vertical +precipices on both sides. The roaming, angry waters are drawn into +whirlpools in one place. They lie stagnant as if sulking in another, +then leap boisterously over ledges of rock and are churned into creamy +foam at the bottom. Outside the mountainous part of its course this same +river flows broad and calm through a mud-banked channel, cut by +tributary streams that draw in the water of low, sloping hills. + +The Missouri is such a wild mountain stream at its headwaters. We who +have seen its muddy waters from Sioux City to St. Louis would hardly +believe that its impetuous and picturesque youth could merge into an old +age so comfortable and placid and commonplace. + +This thing is true of all rivers. They flow, gradually or suddenly, from +higher to lower levels. To reach the lowest level as soon as possible is +the end each river is striving toward. If it could, each river would cut +its bed to this depth at the first stage of its course. Its tools are +the rocks it carries, great and small. The force that uses these tools +is the power of falling water, represented by the current of the stream. +The upper part of a river such as the Missouri or Mississippi engages in +a campaign of widening and deepening its channel, and carrying away +quantities of sediment. The lower reaches of the stream flow through +more level country; the current is checked, and a vast burden of +sediment is laid down. Instead of tearing away its banks and bottom, the +river fills up gradually with mud. The current meanders between banks of +sediment over a bottom which becomes shallower year by year. The Rocky +Mountains are being carried to the Gulf of Mexico. The commerce of the +river is impeded by mountain debris deposited as mud-banks along the +river's lower course. + +Many rivers are quiet and commonplace throughout their length. They flow +between low, rounded hills, and are joined by quiet streams, that occupy +the separating grooves between the hills. This is the oldest type of +river. It has done its work. Rainfall and stream-flow have brought the +level of the land nearly to the level of the stream. Very little more is +left to be ground down and carried away. The landscape is beautiful, but +it is no longer picturesque. Wind and water have smoothed away +unevennesses. Trees and grass and other vegetation check erosion, and +the river has little to do but to carry away the surface water that +falls as rain. + +But suppose our river, flowing gently between its grassy banks, should +feel some mighty power lifting it up, with all its neighbour hills and +valleys, to form a wrinkle in the still unstable crust of the earth. +Away off at the river's mouth the level may not have changed, or that +region may have been depressed instead of elevated by the shrinking +process. Suppose the great upheaval has not severed the upper from the +lower courses of the stream. With tremendous force and speed, the +current flows from the higher levels to the lower. The river in the +highlands strikes hard to reach the level of its mouth. It grinds with +all its might, and all its rocky tools, upon its bed. All the mud is +scoured out, and then the underlying rocks are attacked. If these rocks +are soft and easily worn away, the channel deepens rapidly. One after +another the alternating layers are excavated, and the river flows in a +canyon which deepens more and more. As the level is lowered, the current +of the stream becomes slower and the cutting away of its bed less rapid. +The stream is content to flow gently, for it has almost reached the old +level, on which it flowed before the valley became a ridge or +table-land. + +The rivers that flow in canyons have been thousands of years in carving +out their channels, yet they are newer, geologically speaking, than the +streams that drain the level prairie country. The earth has risen, and +the canyons have been carved since the prairies became rolling, level +ground. + +[Illustration: This little pond is a basin hollowed by the same glacier +that scattered the stones and rounded the hills] + +[Illustration: Every stream is wearing away its banks, while trees and +grass blades are holding on to the soil with all their roots] + +The Colorado River flows through a canyon with walls that in places +present sheer vertical faces a mile in depth, and so smooth that no +trail can be found by which to reach from top to bottom. The region has +but slight erosion by wind, and practically none by rain. The local +rainfall is very slight. So the river is the one force that has acted to +cut down the rocks, and its force is all expended in the narrow area of +its own bed. Had frequent rains been the rule on the Colorado plateau, +the angles of the mesas would have been rounded into hills of the +familiar kind so constantly a part of the landscape in the eastern half +of the continent. + +The Colorado is an ancient river which has to carry away the store of +moisture that comes from the Pacific Ocean and falls as snow on the high +peaks of the Rocky Mountains. Similar river gorges with similar stories +to tell are the Arkansas, the Platte, and the Yellowstone. All cut their +channels unaided through regions of little rain. + +When the earth's crust is thrown up in mountain folds, and between them +valleys are formed, the level of rivers is sometimes lowered and the +rapidity of their flow is checked. A stream which has torn down its +walls at a rapid rate becomes a sluggish water-course, its current +clogged with sediment, which it has no power to carry farther. When such +a river begins to build and obstruct its own waters it bars its progress +and may form a lake as the outlet of its tributary streams. Many ancient +rivers have been utterly changed and some obliterated by general +movements of the earth's crust. + + + + +THE STORY OF A POND + + +Look out of the car window as you cross a flat stretch of new prairie +country, and you see a great many little ponds of water dotting the +green landscape. Forty years ago Iowa was a good place to see ponds of +all shapes and sizes. The copious rainfall of the early spring gathered +in the hollows of the land, and the stiff clay subsoil prevented the +water from soaking quickly into the ground. The ponds might dry away +during the hot, dry summer, leaving a baked clay basin, checked with an +intricate system of cracks. Or if rains were frequent and heavy, they +might keep full to the brim throughout the season. + +Tall bulrushes stood around the margins of the largest ponds, and +water-lilies blossomed on the surface during the summer. The bass and +the treble of the spring chorus were made by frogs and toads and little +hylas, all of which resorted to the ponds to lay their eggs, in coiled +ropes or spongy masses, according to their various family traditions. On +many a spring night my zooelogy class and I have visited the squashy +margins of these ponds, and, by the light of a lantern, seen singing +toads and frogs sitting on bare hummocks of grass roots that stood +above the water-line. The throat of each musician was puffed out into a +bag about the size and shape of a small hen's egg; and all were singing +for dear life, and making a din that was almost ear-splitting at close +range. So great was the self-absorption of these singers that we could +approach them, daze them with the light of the lantern, and capture any +number of them with our long-handled nets before they noticed us. But it +was not easy to persuade them to sing in captivity, no matter how many +of the comforts of home we provided in the school aquariums. So, after +some very interesting nature studies, we always carried them back and +liberated them, where they could rejoin their kinsfolk and neighbours. + +It was when we were scraping the mud from our rubber boots that we +realized the character of the bottoms of our prairie ponds. The slimy +black deposit was made partly of the clay bottom, but largely of +decaying roots and tops of water plants of various kinds. Whenever it +rained or the wind blew hard, the bottom was stirred enough to make the +water muddy; and on the quietest days a pail of pond water had a tinge +of brown because there were always decaying leaves and other rubbish to +stain its purity. + +The farmers drained the ponds as fast as they were able, carrying the +water, by open ditches first, and later by underground tile drains, to +lower levels. Finally these trunk drain pipes discharged the water into +streams or lakes. To-day a large proportion of the pond areas of Iowa +has disappeared; the hollow tile of terra-cotta has been the most +efficient means of converting the waste land, covered by ponds, into +fertile fields. + +But the ponds that have not been drained are smaller than they used to +be, and are on the straight road to extinction. This process one can see +at any time by visiting a pond. Every year a crop of reeds and a dozen +other species of vigorous water plants dies at the top and adds the +substance of their summer growth to the dust and other refuse that +gathers in the bottom of the pond. Each spring roots and seeds send up +another crop, if possible more vigorous than the last, and this top +growth in turn dies and lies upon the bottom. The pond level varies with +the rainfall of the years, but it averages a certain depth, from which +something is each year subtracted by the accumulations of rotting +vegetable matter in the bottom. Evaporation lowers the water-level, +especially in hot, dry summers. From year to year the water plants draw +in to form a smaller circle, the grassy meadow land encroaches on all +sides. The end of the story is the filling up of the pond basin with the +rotting substance of its own vegetation. This is what is happening to +ponds and inland marshes by slow degrees. The tile drain pipes +obliterate the pond in a single season. Nature is more deliberate. She +may require a hundred years to fill up a single pond which the farmer +can rid himself of by a few days of work and a few rods of tiling. + + + + +THE RIDDLE OF THE LOST ROCKS + + +Outside of my window two robins are building a nest in the crotch of a +blossoming red maple tree. And just across the hedge, men are digging a +big square hole in the ground--the cellar of our neighbour's new house. +It looks now as if the robins would get their house built first, for +they need but one room, and they do not trouble about a cellar. I shall +watch both houses as they grow through the breezy March days. + +The brown sod was first torn up by a plough, which uncovered the red New +Jersey soil. Two men, with a team hitched to a scraper, have carried +load after load of the loose earth to a heap on the back of the lot, +while two other men with pickaxes dug into the hard subsoil, loosening +it, so that the scraper could scoop it up. + +This subsoil is heavy, like clay, and it breaks apart into hard clods. +At the surface the men found a network of tree roots, about which the +soil easily crumbled. Often I hear a sharp, metallic stroke, unlike the +dull sound of the picks striking into the earth. The digger has struck a +stone, and he must work around it, pry it up and lift it out of the way. +A row of these stones is seen at one side of the cellar hole, ranged +along the bank. They are all different in size and shape, and red with +clay, so I can't tell what they are made of. But from this distance I +see plainly that they are irregular in form and have no sharp corners. +The soil strewn along the lot by the scraper is full of stones, mostly +irregular, but some rounded; some are as big as your head, others grade +down to the sizes of marbles. + +When I went down and examined this red earth, I found pebbles of all +shapes and sizes, gravel in with the clay, and grains of sand. This +rock-sprinkled soil in New Jersey is very much like soil which I know +very well in Iowa; it looks different in colour, but those pebbles and +rock fragments must be explained in the same way here as there. + +These are not native stones, the outcrop of near-by hillsides, but +strangers in this region. The stones in Iowa soil are also imported. + +The prairie land of Iowa has not many big rocks on the surface, yet +enough of them to make trouble. The man who was ploughing kept a sharp +lookout, and swung his plough point away from a buried rock that showed +above ground, lest it should break the steel blade. One of the farmer's +jobs for the less busy season was to go out with sledge and dynamite +sticks, and blast into fragments the buried boulders too large to move. +Sometimes building a hot fire on the top of it, and throwing on water, +would crack the stubborn "dornick" into pieces small enough to be loaded +on stone-boats. + +I remember when the last giant boulder whose buried bulk scarcely showed +at the surface, was fractured by dynamite. Its total weight proved to be +many tons. We hauled the pieces to the great stone pile which furnished +materials for walling the sides of a deep well and for laying the +foundation of the new house. Yet for years stones have been +accumulating, all of them turned out of the same farm, when pastures and +swampy land came under the plough. + +Draw a line on the map from New York to St. Louis, and then turn +northward a little and extend it to the Yellowstone Park. The +boulder-strewn states lie north of this line, and are not found south of +it, anywhere. Canada has boulders just like those of our Northern +States. The same power scattered them over all of the vast northern half +of North America and a large part of Europe. + +What explanation is there for this extensive distribution of unsorted +debris? + + + + +THE QUESTION ANSWERED + + +The rocks tell their own story, partly, but not wholly. They told just +enough to keep the early geologists guessing; and only very recently has +the guessing come upon the truth. + +These things the rocks told: + +1. We have come from a distance. + +2. We have had our sharp corners worn off. + +3. Many of us have deep scratches on our sides. + +4. At various places we have been dumped in long ridges, mixed with much +earth. + +5. A big boulder is often balanced on another one. + +The first thing the geologist noted was the fact that these boulders are +strangers--that is, they are not the native rocks that outcrop on +hillsides and on mountain slopes near where they are found. Far to the +north are beds of rock from which this debris undoubtedly came. Could a +flood have scattered them as they are found? No, for water sorts the +rock debris it deposits, and it rounds and polishes rock fragments, +instead of scratching and grooving them and leaving them angular, as +these are. + +Professor Agassiz went to Switzerland and studied the glaciers. He found +unsorted rock fragments where the glacier's nose melted, and let them +fall. They were worn and scratched and grooved, by being frozen into the +ice, and dragged over the rocky bed of the stream. The rocky walls of +the valley were scored by the glacier's tools. Rounded domes of rock +jutted out of the ground, in the paths of the ice streams, just like the +granite outcrop in Central Park in New York, and many others in the +region of scattered boulders. + +After long studies in Europe and in North America, Professor Agassiz +declared his belief that a great ice-sheet once covered the northern +half of both countries, rounding the hills, scooping out the valleys and +lake basins, and scattering the boulders, gravel, and clay, as it +gradually melted away. + +The belief of Professor Agassiz was not accepted at once, but further +studies prove that he guessed the riddle of the boulders. The rich soil +of the Northern States is the glacial drift--the mixture of rock +fragments of all sizes with fine boulder clay, left by the gradual +melting of the great ice-sheet as it retreated northward at the end of +the "Glacial Epoch." + + + + +GLACIERS AMONG THE ALPS + + +Switzerland is a little country without any seacoast, mountainous, with +steep, lofty peaks, and narrow valleys. The climate is cool and moist, +and snow falls the year round on the mountain slopes. A snow-cap covers +the lower peaks and ridges. Above the level of nine thousand feet the +bare peaks rise into a dry atmosphere; but below this altitude, and +above the six thousand-foot mark, lies the belt of greatest snowfall. +Peaks between six and nine thousand feet high are buried under the +Alpine snow-field, which adds thickness with each storm, and is drained +away to feed the rushing mountain streams in the lower valleys. + +The snow that falls on the steep, smooth slope clings at first; but as +the thickness and the weight of these snow banks increase, their hold on +the slope weakens. They may slip off, at any moment. The village at the +foot of the slope is in danger of being buried under a snow-slide, which +people call an avalanche. "Challanche" is another name for it. The +hunter on the snow-clad mountains dares not shout for fear that his +voice, reechoing among the silent mountains, may start an avalanche on +its deadly plunge into the valley. + +On the surface of the snow-field, light snow-flakes rest. Under them the +snow is packed closer. Deeper down, the snow is granular, like pellets +of ice; and still under this is ice, made of snow under pressure. The +weight of the accumulated snow presses the underlying ice out into the +valleys. These streams are the glaciers--rivers of ice. + +The glaciers of the Alps vary in length from five to fifteen miles, from +one to three miles in width, and from two hundred to six hundred feet in +thickness. They flow at the rate of from one to three feet a day, going +faster on the steeper slopes. + +It is hard to believe that any substance as solid and brittle as ice can +flow. Its movement is like that of stiff molasses, or wax, or pitch. The +tremendous pressure of the snow-field pushes the mass of ice out into +the valleys, and its own weight, combined with the constant pressure +from behind, keeps it moving. + +The glacier's progress is hindered by the uneven walls and bed of the +valley, and by any decrease in the slope of the bed. When a flat, broad +area is reached, a lake of ice may be formed. These are not frequent in +the Alps. The water near the banks and at the bottom of a river does not +flow as swiftly as in the middle and at the surface of the stream. The +flow of ice in a glacier is just so. Friction with the banks and bottom +retards the ice while the middle parts go forward, melting under the +strain, and freezing again. There is a constant readjusting of +particles, which does not affect the solidity of the mass. + +The ice moulds itself over any unevenness in its bed if it cannot remove +the obstruction. The drop which would cause a small waterfall in a +river, makes a bend in the thick body of the ice river. Great cracks, +called _crevasses_, are made at the surface, along the line of the bend. +The width of the V-shaped openings depends upon the depth of the glacier +and the sharpness of the bend that causes the breaks. + +Rocky ridges in the bed of the ice-stream may cause crevasses that run +lengthwise of the glacier. Snow may fill these chasms or bridge them +over. The hunter or the tourist who ventures on the glacier is in +constant danger, unless he sees solid ice under him. Men rope themselves +together in climbing over perilous places, so that if one slips into a +crevasse his mates can save him. + +A glacier tears away and carries away quantities of rock and earth that +form the walls of its bed. As the valley narrows, tremendous pressure +crowds the ice against the sides, tearing trees out by the roots and +causing rock masses to fall on the top of the glacier, or to be dragged +along frozen solidly into its sides. The weight of the ice bears on the +bed of the glacier, and its progress crowds irresistibly against all +loose rock material. The glacier's tools are the rocks it carries frozen +into its icy walls and bottom. These rocks rub against the walls, +grinding off debris which is pushed or carried along. No matter how +heavy the boulders are that fall in the way of the ice river, the ice +carries them along. It cannot drop them as a river of water would do. +Slowly they travel, and finally stop where the nose of the glacier melts +and leaves all debris that the mountain stream, fed by the melting of +the ice, cannot carry away. + +The bedrock under a glacier is scraped and ground and scored by the +glacier's tools--the rock fragments frozen into the bottom of the ice. +These rocks are worn away by constant grinding, just as a steel knife +becomes thin and narrow by use. Scratches and scorings and polished +surfaces are found in all rocks that pass one another in close contact. +Its worn-out tools the glacier drops at the point where its ice melts. +This great, unsorted mass of rock meal and coarser debris the stream is +gradually scattering down the valley. + +The name "moraine" has been given to the earth rubbish a glacier +collects and finally dumps. The _top moraine_ is at the surface of the +ice. The _lateral moraines_, one at each side, are the debris gathered +from the sides of the valley. The _ground moraine_ is what debris the +ice pushes and drags along on the bottom. The _terminal moraine_ is the +dumping-ground of this mass of material, where the ice river melts. + +Glaciers, like other rivers, often have tributary streams. A _median +moraine_, seen as a dark streak running lengthwise on the surface of a +glacier, means that two branch glaciers have united to form this one. Go +back far enough and you will reach the place where the two streams come +together. The two lateral moraines that join form the middle line of +debris, the median moraine. Three ice-streams joined produce two top +moraines. They locate the lateral moraines of the middle glacier. + +The surface of a glacier is often a mass of broken and rough ice, +forming a series of pits and pinnacles that make crossing impossible. +The sun melts the surface, forming pools and percolating streams of +water, that honeycomb the mass. Underneath, the ice is tunnelled, and a +rushing stream flows out under the end of the glacier. It is not clear, +but black with mud, called _boulder clay_, or _till_, made of ground +rock, and mixed with fragments of all shapes and sizes. This is the meal +from the glacier's mill, dumped where the water can sift it. + +"Balanced rocks" are boulders, one upon another, that once lay on a +glacier, and were left in this strange, unstable position when the +supporting ice walls melted away from them. In Bronx Park in New York +the "rocking stone" always attracts attention. The glacier that lodged +it there, also rounded the granite dome in Central Park and scattered +the rock-strewn boulder clay on Long Island. Doubtless in an earlier day +the edges of this glacier were thrust out into the Atlantic, not far +from the Great South Bay, and icebergs broke off and floated away. + +[Illustration: Potsdam sandstone showing ripple marks] + +[Illustration: _By permission of the American Museum of Natural History_ + +Glacial striae on Lower Helderberg limestone] + +[Illustration: Glacial grooves in the South Meadow, Central Park, New +York] + +[Illustration: _By permission of the American Museum of Natural History_ + +Mt. Tom, West 83d St., New York] + +Glaciers are small to-day compared with what they were long ago, in +Europe and in America. The climate became warmer, and the ice-cap +retreated. Old moraines show that the ice rivers of the Alps once came +much farther down the valleys than they do now. Smooth, deeply scored +domes of rock, the one in Central Park and the bald head of Mount Tom, +are just like those that lie in Alpine valleys from which the glaciers +have long ago retreated. There are old moraines far up the sides of +valleys, showing that once the glaciers were far deeper than now. No +other power could have brought rocks from strata higher up the +mountains, and lodged them thus. + +Nearer home, Mt. Shasta and Mt. Rainier still have glaciers that have +dwindled in size, until they bear little comparison to the gigantic +ice-streams that once filled the smooth beds their puny successors flow +into. Remnants of glaciers lie in the hollows of the Sierras. We must go +north to find the snow-fields of Alaska and glaciers worthy to be +compared with those ancient ice rivers whose work is plainly to be seen, +though they are gone. + + + + +THE GREAT ICE-SHEET + + +Greenland is green only along its southern edge, and only in summer, so +its name is misleading. It is a frozen continent lying under a great +ice-cap, which covers 500,000 square miles and is several thousand feet +in thickness. The top of this icy table-land rises from five thousand to +ten thousand feet above the sea-level. The long, cold winters are marked +by great snowfall, and the drifts do not have time to melt during the +short summer; and so they keep getting deeper and deeper. Streams of ice +flow down the steeps into the sea, and break off by their weight when +they are pushed out into the water. These are the icebergs which float +off into the North Atlantic, and are often seen by passengers on +transatlantic steamers. + +Long ago Greenland better deserved its name. Explorers who have climbed +the mountain steeps that guard the unknown ice-fields of the interior +have discovered, a thousand feet above the sea-level, an ancient beach, +strewn with shells of molluscs like those which now inhabit salt water, +and skeletons of fishes lie buried in the sand. It is impossible to +think that the ocean has subsided. The only explanation that accounts +for the ancient beach, high and dry on the side of Greenland's icy +mountain is that the continent has been lifted a thousand feet above its +former level. This is an accepted fact. + +We know that climate changes with changed altitude as well as latitude. +Going up the side of a mountain, even in tropical regions, we may reach +the snow-line in the middle of summer. Magnolia trees and tree ferns +once grew luxuriantly in Greenland forests. Their fossil remains have +been found in the rocks. This was long before the continent was lifted +into the altitude of ice and snow. And it is believed that the climate +of northern latitudes has become more severe than formerly from other +causes. It is possible that the earth's orbit has gradually changed in +form and position. + +If Greenland should ever subside until the ancient beach rests again at +sea-level, the secrets of that unknown land would be revealed by the +melting of the glacial sheet that overspreads it. Possibly it would turn +out to be a mere flock of islands. We can only guess. North America had, +not so long ago, two-thirds of its area covered with an ice-sheet like +that of Greenland, and a climate as cold as Greenland's. At this time +the land was lifted two to three thousand feet higher than its present +level. All of the rain fell as snow, and the ice accumulated and became +thicker year by year. Instead of glaciers filling the gorges, a great +ice flood covered all the land, and pushed southward as far as the Ohio +River on the east and Yellowstone Park in the west. The Rocky Mountains +and some parts of the Appalachian system accumulated snow and formed +local glaciers, separated from the vast ice-sheet. + +The unstable crust of the earth began to sink at length, and gradually +the ice-sheet's progress southward was checked, and it began to recede +by melting. All along the borders of this great fan-shaped ice-field +water accumulated from the melting, and flooded the streams which +drained it to the Atlantic and the Gulf. Icebergs broken off of the edge +of the retiring ice-sheet floated in a great inland sea. The land sank +lower and lower until the general level was five hundred to one thousand +feet lower than it now is. The climate became correspondingly warm, and +the icebergs melted away. Then the land rose again, and in time the +inland sea was drained away into the ocean, except for the waters that +remained in thousands of lakes great and small that now occupy the +region covered by the ice. + +Ancient sea beaches mark the level of high water at the time that the +flood followed the melting ice. On the shores of Lake Champlain, but +nearly five hundred feet higher than the present level of the lake, +curious geologists have found many kinds of marine shells on a +well-marked old sea beach. The members of one exploring party in the +same region were surprised and delighted to come by digging upon the +skeleton of a whale that had drifted ashore in the ancient days when +the inland sea joined the Atlantic. + +Lake Ontario's ancient beach is five hundred feet above the present +water-level; Lake Erie's is two hundred fifty feet above it; Lake +Superior's three hundred thirty feet higher than the present beach. No +doubt when the water stood at the highest level, the Great Lakes formed +one single sheet of water which settled to a lower level as the rivers +flowing south cut their channels deep enough to draw off the water +toward the Gulf. Lake Winnipeg is now the small remnant of a vast lake +the shores of which have been traced. The Minnesota River finally made +its way into the Mississippi and drained this great area the stranded +beaches of which still remain. The name of Agassiz has been given to the +ancient lake formed by the glacial flood and drained away thousands of +years ago but not until it had built the terraced beach which locates it +on the geological map of the region. + +When the ice-sheet came down from the north it dragged along all of the +soil and loose rock material that lay in its path. With the boulders +frozen into its lower surface it scratched and grooved the firm bedrock +over which it slid, and rounded it to a smooth and billowy surface. The +progress of the ice-sheet was southward, but it spread like a fan so +that its widening border turned to east and west. + +When it reached its southernmost limit and began to melt, it laid down a +great ridge of unsorted rock material, remnants of which remain to this +day,--the terminal moraine of the ancient ice-sheet. The line of this +ancient deposit starts on Long Island, crosses New Jersey and +Pennsylvania, then dips southward, following the general course of the +Ohio River to its mouth, forming bluffs in southern Ohio, Indiana, and +Illinois. The line bends upward as it crosses central Missouri, a corner +of Kansas, and eastern Nebraska, parallel with the course of the +Missouri. + +As the ice-sheet melted, boulders were dropped all over the Northern +States and Canada. These were both angular and rounded. In some places +they are scattered thickly over the surface and are so numerous as to be +a great hindrance to agriculture. In many places great boulders of +thousands of tons weight are perched on very slight foundations, just +where they lodged when the ice went off and left them, after carrying +them hundreds of miles. Around them are scattered quantities of loose +rock material, not scored or ground as are those which were carried on +the under-surface of the glacial ice. These unscarred fragments rode on +the top of the ice. They were a part of the top moraine of the glacial +sheet. + +The finest material deposited is rock meal, ground by the great glacial +mill, and called "boulder clay." It is a stiff, dense, stony paste in +which boulders of all sizes, gravel, pebbles, and cobblestones are +cemented. + +The "drift" of the ice-sheet is the rubbish, coarse and fine, it left +behind as it retreated. Below the Ohio River there is a deep soil +produced by the decay of rocks that lie under it. North of Ohio is +spread that peculiar mixture of earth and rock fragments which was +transported from the north and spread over the land which the ice-sheet +swept bare and ground smooth and polished. + +The drift has been washed away in places by the floods that followed the +ice. Granite domes are thus exposed, the grooves and scratches of which +tell in what direction the ice flood was travelling. Miles away from +that scored granite, but in the same direction as the scratches, +scattered fragments of the same foundation rock cover fields and +meadows. Thus, much of the drift material can be traced to its original +home, and the course of the ice-sheet can be determined. Many immense +boulders the home of which was in the northern highlands of Canada rode +southward, frozen into icebergs that floated in the great inland sea. +Great quantities of debris were added to the original glacial drift +through the agency of these floating ice masses, which melted by slow +degrees. + + + + +FOLLOWING SOME LOST RIVERS + + +What would you think if the boat in which you were floating down a +pleasant river should suddenly grate upon sand, and you should look over +the gunwale and find that here the waters sank out of sight, the river +ended? I believe you would rub your eyes, and feel sure that you were +dreaming. Do not all rivers flow along their beds, growing larger with +every mile, and finally empty their waters into a sea, or bay, or lake, +or flow into some larger stream? This is the way of most rivers, but +there are exceptions. In the Far West there are some great rivers that +absolutely disappear before they reach a larger body of water. They +simply sink away into the sand, and sometimes reappear to finish their +courses after flowing underground for miles. Do you know the name of one +great western river of which I am thinking? Is there any stream in your +neighbourhood which has such peculiar ways? + +Down in Kentucky there is a region where, it is said, one may walk fifty +miles without crossing running water. In the middle of our country, in +the region of plentiful rainfall, and in a state covered with beautiful +woodlands and famous for blue grass and other grain crops, it is +amazing that, over a large area, brooks and larger streams are lacking. +In most of the state there is plenty of water flowing in streams like +those in other parts of the eastern half of the United States. In the +near neighbourhood of this peculiar section of the state the streams +come to an end suddenly, pouring their water into funnel-shaped +depressions of the ground called sink-holes. After a heavy rain the +surface water, accumulating in rivulets, may also be traced to small +depressions which seem like leaks in the earth's crust, into which the +water trickles and disappears. + +It must have been noticed by the early settlers who came over the +mountains from the eastern colonies, and settled in the new, wild, hilly +country, which they called Kentucky. The first settlers built their log +cabins along the streams they found, and shot deer and wild turkey and +other game that was plentiful in the woods. The deer showed them where +salt was to be found in earthy deposits near the streams; for salt is +necessary to every creature. Deer trails led from many directions to the +"salt licks" which the wild animals visited frequently. + +Perhaps the same pioneers who dug the salt out of the earth found +likewise deposits of _nitre_, called also _saltpetre_, a very precious +mineral, for it is one of the elements necessary in the manufacture of +gunpowder. With the Indians all about him, and often showing themselves +unfriendly, the pioneer counted gunpowder a necessity of life. He relied +on his gun to defend and to feed his family. There were men among those +first settlers who knew how to make gunpowder, and saltpetre was one of +the things that had to be carried across the mountains into Kentucky, +until they found it in the hills. No wonder that prospectors went about +looking for nitre beds in the overhanging ledges of rocks along +stream-beds. In such situations the deposits of nitre were found. The +earth was washed in troughs of running water to remove the clayey +impurity. After a filtering through wood-ashes, the water which held the +nitre in solution was boiled down, and left to evaporate, after which +the crystals of saltpetre remained. + +Solid masses of saltpetre weighing hundreds of pounds were sometimes +found in protected corners under shelving rocks. It was no doubt in the +fascinating hunt for lumps of this pure nitre that the early prospectors +discovered that the streams which disappeared into the sink-holes made +their way into caverns underground. Digging in the sides of ravines +often made the earthy wall cave in, and the surprised prospector stood +at the door of a cavern. The discoverer of a cave had hopes that by +entering he might find nitre beds richer than those he could uncover on +the surface, and this often turned out to be true. The hope of finding +precious metals and beds of iron ore also encouraged the exploration of +these caves. By the time the war of 1812 was declared, the mining of +saltpetre was a good-sized industry in Kentucky. Most of the mineral was +taken out of small caves, and shipped, when purified, over the +mountains, on mule-back by trails, and in carts over good roads that +were built on purpose to bring this mineral product to market. As long +as war threatened the country, the Government was ready to buy all the +saltpetre the Kentucky frontiersmen could produce. And the miners were +constantly in search of richer beds that promised better returns for +their labour. + +It was this search that led to the exploration of the caves discovered, +although the explorer took his life in his hands when he left the +daylight behind him and plunged into the under-world. + +Not all lost rivers tell as interesting stories or reveal as valuable +secrets as did those the neighbours of Daniel Boone traced along their +dark passages underground, and finally saw emerge as hillside springs, +in many cases, to feed Kentucky rivers. But it is plain that no river +sinks from sight unless it finds porous or honeycombed rocks that let it +through. The water seeks the nearest and easiest route to the sea. Its +weight presses toward the lowest level, always. The more water absorbs +of acid, the more powerfully does it attack and carry away the substance +of lime rocks through which it passes. + + + + +THE MAMMOTH CAVE OF KENTUCKY + + +There is no more fertile soil in the country than that of the famous +blue grass region of Kentucky. The surface soil rests upon a deep +foundation of limestone rocks, and very gradually the plant food locked +up in these underlying strata is pulled up to the surface by the soil +water, and greedily appropriated by the roots of the plants. + +Part of the water of the abundant rainfall of this region soaks into the +layers of the lime rock, carrying various acids in solution which give +it power to dissolve the limestone particles, and thus to make its way +easily through comparatively porous rock to the very depths of the +earth. So it has come about that the surface of the earth is undermined. +Vast empty chambers have been carved by the patient work of trickling +water, which has carried away the lime that once formed solid and +continuous layers of the earth's crust. We must believe that the work +has taken thousands of years, at least, for no perceptible change has +come to these wonderful caves since the discovery and exploration of +them a century and more ago. + +The streams that flow into the region of these caves disappear suddenly +into sink-holes and flow through caverns. After wearing away their +subterranean channels, leaping down from one level to another, forming +waterfalls and lakes, some emerge finally through hillsides in the form +of springs. + +The cavern region of Kentucky covers eight thousand square miles. The +underground chambers found there are in the limestone rock which varies +from ten to four hundred feet in thickness, and averages a little less +than two hundred feet. Over this territory the number of sink-holes +average one hundred to the square mile; and the streams that have poured +their water into these basins have made a network of open caverns one +hundred thousand miles in length. + +A great many small caverns have been thoroughly explored and are famous +for their beauty. The Diamond Cave is one of the most splendid, for it +is lined with walls and pillars of alabaster that sparkle in the +torchlight with crystals that look like veritable diamonds. Beautiful +springs and waterfalls are found in many caves, but the grandest of all +is the Mammoth Cave, beside which no other is counted worthy to be +compared. + +Great tales the miners told of the wonder and the beauty of these +caverns, the walls of which were supported by arching alabaster columns +and wonderful domes, of indescribable beauty of form and colouring. In +1799, the year that Washington died, a pioneer discovered the entrance +to a cave, the size and beauty of which surpassed anything he had seen +before. After exploring it for a short distance he returned home and +took his whole family with him to enjoy the first view of the wonderful +cavern he had discovered. They carried pine knots and a lighted torch, +by which they made their way for some distance, but the torch was +accidentally extinguished and they groped their way in darkness and +missed the entrance. Without anything to guide them, they wandered in +darkness for three days, and were almost dead when at last they stumbled +upon the exit. This is the doorway of the Mammoth Cave of Kentucky, one +of the wonders of the world. + +This was a terrible experience. The next persons who attempted to +explore the new cave were better provisioned against the chance of +spending some time underground. The pioneers found rich deposits of +nitre in the "Great Cave," as they called it. Scientists visited it and +explored many of its chambers. The reputation of this cavern has been +spread by thousands of visitors who have come from all over the world to +see it. The cave has not yet been completely explored. The regular +tours, on which the guides conduct visitors, cover but a small part of +the one hundred and fifty miles measured by the two hundred or more +avenues. The passages wind in and out, crossing each other, sometimes at +different levels, and forming a network of avenues in which the +unaccustomed traveller would surely be lost. The old guides know every +inch of their regular course, and their quaint and edifying talk adds +greatly to the pleasure of the visitors. + +From the hotel, parties are organized for ten o'clock in the morning and +seven o'clock in the evening. Each visitor is provided with a lard-oil +lamp. The guide carries a flask of oil and plenty of matches. No special +garb is necessary, though people usually dress for comfort, and wear +easy shoes. The temperature of the cave is uniform winter and summer, +varying between fifty-three and fifty-four degrees Fahrenheit. + +The cave entrance is an arch of seventy-foot span in the hillside. A +winding flight of seventy stone steps leads the party around a +waterfall, into a great chamber under the rocks. Then the way goes +through a narrow passage, where the guide unlocks an iron gate to let +them in. The visitors now leave all thoughts of daylight behind, for the +breeze that put out their lights as they entered the cave is past, and +they stand in the Rotunda, a vast high-ceilinged chamber, silent and +impressive, with walls of creamy limestone, encrusted with gypsum, which +has been stained black by manganese. From the vestibule on, each passage +and each room has a name, based upon some historic event or some fancied +resemblance. The Giant's Coffin is a great kite-shaped rock lying in one +of the rooms of the cave. The Star Chamber has a wonderful +crystal-studded dome in which the guide produces the effect of a sunrise +by burning coloured lights. Bonfires built at suitable points produce +wonderful shadow effects, which are like nothing else in the world. The +old saltpetre vats which the visitors pass in taking the "Long Route" +through the cave, point them back to the days during the War of 1812, +when this valuable mineral was extracted from the earth in the floor of +the cave. The industry greatly enriched the thrifty owners of the cave, +but the works were abandoned after peace was declared. + +It must be a wonderful experience to walk steadily for nine hours over +the Long Route, for so pure is the air and so wonderful is the scenery +that people rarely complain of fatigue when the experience is over. +There is no dust on the floors of these subterranean chambers, and they +are not damp except near places where water trickles, here and there, in +rivulets and cascades. Pools of water at the bottoms of pits so deep +that a lighted torch requires several seconds to reach the bottom, and +rivers and lakes of considerable size, show where some of the surface +water goes to. A strange underground suction creates whirlpools in some +of these streams. People go in boats holding twenty passengers for a row +on Echo River, and the guide dips up with a net the blind fish and +crayfish and cave lizards which inhabit these subterranean waters. The +echoes in various chambers of the Mammoth Cave are remarkable. In some +of them a song by a single voice comes back with full chords, as if +several voices carried the different parts. The single notes of flute +and cornet are returned with the same beautiful harmonies. A pistol shot +is given back a dozen times, the sound rebounding like a ball from rock +to rock of the arching walls. The vibrations of the water made by the +rower's paddles reecho in sounds like bell notes, and they are +multiplied into harmonies that suggest the chimes in the belfry of a +cathedral. + +The walls of various chambers differ from each other according to the +minerals that compose them. Some are creamy white limestone arches, some +are walled with black gypsum, some are hung with great curtains of +stalagmites, solid but suggesting the lightness and grace of folds of +crepe. Under such hangings the floor is built up in stalactites. The +mineral-laden water, the constant drip of which has produced a hanging, +icicle-like stalagmite, has built up the stalactite to meet it. + +Probably nothing is more beautiful than the flower-like crystals that +bloom all over the walls of a chamber called "Mary's Bower." The floor, +even, sparkles with jewels that have fallen from the wonderful and +delicate flower clusters built from deposits of the lime-laden water +which goes on building and replacing the bits that fall. "Martha's +Vineyard" is decorated with nodules, like bunches of grapes, that +glisten as if the dew were on them. The white gypsum in some caves makes +the walls look as if they were carved out of snow. Still others have +clear, transparent crystals that make them gleam in the torches' light +as if the walls were encrusted with diamonds. + +The cave region of Indiana is also famous. The great Wyandotte Cave in +Crawford County is the most noted of many similar caverns. In some of +the chambers, bats are found clinging to the ceiling, heads downward, +like swarms of bees. The caverns of Luray, in Virginia, are complex and +wonderful in their structure, and famous for the beautiful stalactites +and stalagmites they contain. But there is no cave in this country so +wonderful and so grand in its dimensions as the Mammoth Cave in +Kentucky. + + + + +LAND-BUILDING BY RIVERS + + +Once a year, when the rainy season comes in the mountainous country +south of Egypt, the old Nile floods its banks and spreads its slimy +waters over the land, covering the low plains to the very edge of the +Sahara Desert. The people know it is coming, and are prepared for this +flood. We should think such an overflow of our nearest river a monstrous +calamity, but the Egyptians bless the river which blesses them. They +know that without the Nile's overflow their country would be added to +the Desert of Sahara. In a short time after the overflow, the river +reaches its highest point and begins to ebb. Canals lying parallel to +its course are filled with water which is saved for use in the hot, dry +summer. As the flood goes down, a deposit of slimy mud lies as a rich +fertilizer on the land. It is this and the water which the earth has +absorbed that make Egypt one of the most fertile agricultural countries +in the world. + +The region covered by the Nile's overflow is the flood plain of this +river. On this plain the Pyramids, the Sphinx, and other famous +monuments of Egypt stand. The statue of Rameses II. built 3,000 years +ago, has its base buried nine feet deep in the rich soil made of Nile +sediment. A well dug in this region goes through forty feet of this soil +before striking the underlying sand. How many years ago did the first +Nile overflow take place? We may begin our calculation by finding out +the average yearly deposit. It is a slow process that accumulates but +nine feet in 3,000 years. If you were in Egypt when the Nile went back +into its banks, you would see that the scum it leaves in a single +overflow adds not a great deal to the thickness of the soil. Possibly +floods have varied in their deposits from year to year, so that any +calculation of the time it took to build that forty feet of surface soil +must be but a rough estimate. This much we know: it has been an +uninterrupted process which has taken place within the present +geological epoch, "the Age of Man." + +Not all the rich sediment the Nile brings down is left on the level +flood plain along its course. A vast quantity is dumped at the river's +mouth, where the tides of the Mediterranean check the river's current. +Thus the great delta is formed. The broad river splits into many mouths +that spread out like a fan and build higher and broader each year the +mud-banks between the streams. Upper Egypt consists of river swamps. +Lower Egypt, from Cairo to the sea, is the delta built by the river +itself on sea bottom. From the head of the delta, where the river +commences to divide, to the sea, is an area of 10,000 square miles made +out of material contributed by upper Egypt, and built by the river. +Layer upon layer, it is constantly forming, but most rapidly during the +season of floods. + +Coming closer home, let us look at the map of the Mississippi Valley. +Begin as far north as St. Louis. For the rest of its course the +Mississippi River flows through a widening plain of swamp land, flooded +in rainy seasons. Through this swampy flood plain the river meanders; +its current, heavily loaded with sediment, swings from one side to the +other of the channel, building up here, wearing away there, and +straightening its course when the curves become so sharp that their +sides meet. Then the current breaks through the thin wall, and a bayou +of still water is left behind. + +Below Baton Rouge the Mississippi breaks into many mouths, that spread +and carry the water of the great river into the Gulf of Mexico. The Nile +delta is triangular, like delta, [Greek: D], the fourth letter of the +Greek alphabet; but the Mississippi's delta is very irregular. The main +mouth of the river flows fifty miles out into the Gulf between +mud-banks, narrow and low. At the tip it branches into several streams. + +From the mouth of the Ohio to the Gulf, the Mississippi flood plain +covers 30,000 square miles. Over this area, sediment to an average depth +of fifty feet has been laid down. In earlier times the river flooded +this whole area, when freshets swelled its tributaries in the spring. +The flood plain then became a sea, in the middle of which the river's +current flowed swiftly. The slow-flowing water on each side of the main +current let go of its burden of sediment and formed a double ridge. +Between these two natural walls the main river flowed. When its level +fell, two side streams, running parallel with the main river drained the +flood plains on each side into the main tributaries to right and left. +These natural walls deposited when the river was in flood are called +_levees_. Each heavy flood builds them higher, and the bed of the stream +rises by deposits of sediment. So it happens that the level of the river +bed is higher than the level of its flood plain. + +This is an interesting fact in geology. But the people who have taken +possession of the rich flood plain of the Mississippi River, who have +built their homes there, drained and cultivated the land, and built +cities and towns on the areas reclaimed from swamps, recognize the +elevation of the river bed as the greatest danger that threatens them. +Suppose a flood should come. Even if it does not overflow the levees, it +may break through the natural banks and thus overflow the cities and the +farm lands to left and right. + +Instead of living in constant fear of such a calamity, the people of the +Mississippi flood plain have sought safety by making artificial levees, +to make floods impossible. These are built upon the natural levees. As +the river bed rises by the deposit of mud, the levees are built higher +to contain the rising waters. No longer does the rich soil of the +Mississippi flood plain receive layers of sediment from the river's +overflow. The river very rarely breaks through a levee. The United +States Government has spent great sums in walling in the river, and each +state along its banks does its share toward paying for this +self-protection. + +By means of _jetties_ the river's current is directed into a +straightened course, and its power is expended upon the work of +deepening its own channel and carrying its sediment to the Gulf. Much as +the river has been forced to do in cleaning its own main channel, +dredging is needed at various harbours to keep the river deep enough for +navigation. The forests of the mountain slopes in Colorado are being +slaughtered, and the headwaters of the Missouri are carrying more and +more rocky debris to choke the current of the Mississippi. Colorado soil +is stolen to build land in the vast delta, which is pushing out into the +Gulf at the rate of six miles in a century--a mile in every sixteen +years. The Mississippi delta measures 14,000 square miles. With the +continued denuding of mountain slopes, we shall expect the rate of delta +growth to be greatly increased, until reforesting checks the destructive +work of wind and water. + + + + +THE MAKING OF MOUNTAINS + + +The gradual thickening and shrinking of the earth's crust as it cools +have made the wrinkles we call mountain systems. Through millions of +years the globe has been giving off heat to the cold sky spaces through +which it swings in its orbit around the sun. The cooling caused the +contraction of the outer layer to fit the shrinking of the mass. When a +plump peach dries on its pit, the skin wrinkles down to fit the dried +flesh. The fruit shrinks by loss of water, just as the face of an old +person shrinks by loss of fat. The skin becomes wrinkled in both cases. + +The weakest places in the earth's crust were the places to crumple, +because they could not resist the lateral pressure that was exerted by +the shrinking process. Along the shores of the ancient seas the rivers +piled great burdens of sediment. This caused the thin crust to sink and +to become a basin alongside of a ridge. The wearing away of the land in +certain places lightened and weakened the crust at these places, so that +it bent upward in a ridge. + +Perhaps the first wrinkles were not very high and deep. The gradual +cooling must have exerted continued pressure, and the wrinkles have +become larger. It is not likely that new wrinkles would be formed as +long as the old ones would crumple and draw up into narrower, steeper +slopes, in response to the lateral crushing. + +We can imagine those first mountains rising as folds under the sea. +Gradually their bases were narrowed, and their crests lifted out of the +water. They rose as long, narrow islands, and grew in size as time went +on. + +Why is the trend of the great mountain systems almost always north and +south? Study the map of the continents and see how few cross ranges are +shown, and how short they are, compared with the others. The molten +globe bulged at its equator, as it rotated on its axis. The moon added +its strong pulling force to make it bulge still more. As the crust +thickened, it became less responsive to the two forces that caused it to +bulge. The shrinkage was greatest where the globe had been most pulled +out of shape. The rate of the earth's rotation is believed to have +diminished. Every change tended to let the earth draw in its (imaginary) +belt, a notch at a time. The forces of contraction acted along the line +of the equator, and formed folds running toward the poles. In this early +time the great mountain systems were born, and they grew in size +gradually, from small beginnings. + +These mountains of upheaval, made by the bending of the earth's crust, +and the formation of alternating ridges and depressed valleys, are many. +The earth is old and much wrinkled. Other mountains have been formed by +forces quite different. Volcanic mountains have been far more numerous +in ages gone than they are now. + +Mt. Hood and Mt. Rainier are peaks built up by the materials thrown out +of the craters of volcanoes dead these thousands of years. Vesuvius is +at present showing us how volcanic mountains are made. Each eruption +builds larger the cone--that is, the chimney through which the molten +rocks, the ashes, and the steam are ejected. Side craters may open, the +main cone be broken and its form changed, but the mass of lava and +stones and ashes grows with each eruption. The mountain grows by the +additions it receives. AEtna is a mountain built of lava. + +A third mountain system grew, not by addition, but by subtraction. The +Catskills illustrate this type. This group of mountains is the remnant +of a table-land made of level layers of red sandstone. The rest of the +high plain has been cut down and carried away, leaving these picturesque +hills, the survival of which is as much a mystery as the disappearance +of the balance of the plateau of which they were once a part. + +The fold that forms a typical mountain ridge has a cone of granite, the +original rock foundation of the earth, and on this are layers of +stratified rock, ancient deposits of sediment carried to the sea by +streams. When exposed to wind and rain, the ridge is gradually worn +down. In some places the water cuts away the soft rock and forms a +stream-bed, that cuts deeper and deeper, using the rock fragments as its +tools. Often the layers of aqueous rocks are cut through, and the +granite exposed. + +Sometimes the hardest stratified rock-beds resist the water and the wind +and are left as a series of ridges along the sides of the main range. +The crumpling forces may crack the ridge open for its whole length, and +one side of the chasm may slip down and the other go up. The result is a +sheer wall of exposed rock strata, layers of which correspond with those +that lie far below the top of the portion that slid down in the great +upheaval and subsidence that parted them. These slips are known as +_faults_. + + + + +THE LAVA FLOOD OF THE NORTHWEST + + +We know little about the substance that occupies the four thousand miles +of distance between the surface and the centre of our earth. We know +that the terrible weight borne by the central mass compresses it, so +that the interior must grow denser as the core is approached. Scientists +have weighed the earth, and tell us that the crust is lighter than the +rest. The supposition is that there is a great deal of iron in the +interior, and possibly precious metals, too. + +Our deepest wells and mines go down about a mile, then digging stops, on +account of the excessive heat. But the crumpling of the crust, and the +wearing away of the folded strata by wind and running water, have laid +bare rocks several miles in thickness on the slopes of mountains, and +exposed the underlying granite, on which the first sedimentary rocks +were deposited. On this granite lie stratified rocks, which are +crystalline in texture. These are the beds, sometimes miles in depth, +called _metamorphic_ rocks, formed by water, then transformed by heat. + +The wearing away of rocks by wind and water has furnished the materials +out of which the aqueous rocks have been made. Layers upon layers of +sandstone, shales, limestone, and the like, are exposed when a river +cuts a canyon through a plateau. The layered deposits of debris at the +mouth of the river make new aqueous rocks out of old. Every sandy beach +is sandstone in the making. This work is never ended. + +In the early days the earth's crust often gaped open in a mighty crater +and let a flood of lava overspread the surface. The ocean floor often +received this flood of melted rock. In many places the same chimney +opened again and again, each time spreading a new layer of lava on top +of the old, so that the surface has several lava sheets overlying the +aqueous strata. + +If the hardened lava sheet proved a barrier to the rising tide of molten +lava in the chimney it was often forced out in sheets between the layers +of aqueous rocks. Wherever the heated material came into contact with +aqueous rocks it transformed them, for a foot or more, into crystalline, +metamorphic rocks. + +A chimney of lava is called a _dike_. In mountainous countries dikes are +common. Sometimes small, they may also be hundreds of feet across, often +standing high above the softer strata, which rains have worn away. Dikes +often look like ruined walls, and may be traced for miles where they +have been overturned in the mountain-making process. + +The great lava flood of the Northwest happened when the Coast Range was +born. Along the border of the Pacific Ocean vast sedimentary deposits +had accumulated during the Cretaceous and Tertiary Periods. Then the +mighty upheaval came, the mountain ridge rose at the end of the Miocene +epoch and stretched itself for hundreds of miles through the region +which is now the coast of California and Oregon. Great fissures opened +in the folded crust, and floods of lava overspread an area of 150,000 +square miles. A dozen dead craters show to-day where those immense +volcanic chimneys were. The depth of the lava-beds is well shown where +the Columbia River has worn its channel through. Walls of lava three +thousand feet in thickness rise on each side of the river. They are made +of columns of basalt, fitted together, like cells of a honeycomb, and +jointed, forming stone blocks laid one upon another. The lava shrinks on +cooling and forms prisms. In Ireland, the Giants' Causeway is a famous +example of basaltic formation. In Oregon, the walls of the Des Chutes +River show thirty lava layers, each made of vertical basalt columns. The +palisades of the Hudson, Mt. Tom, and Mt. Holyoke are examples on the +eastern side of the continent of basaltic rocks made by lava floods. + +Northern California, northwestern Nevada, and large part of Idaho, +Montana, Oregon, and Washington are included in the basin filled with +lava at the time of the great overflow, which extended far into British +Columbia. It is probable that certain chimneys continued to discharge +until comparatively recent times. Mt. Rainier, Mt. Shasta, and Mt. Hood +are among dead volcanoes. + +Quite a different history has the great Deccan lava-field of India, +which covers a larger area than the basin of our Northwest, and is in +places more than a mile in depth. It has no volcanoes, nor signs of any +ever having existed. The floods alone overspread the region, which shows +no puny "follow-up system" of scattered craters, intermittently in +eruption. + + + + +THE FIRST LIVING THINGS + + +Strange days and nights those must have been on the earth when the great +sea was still too hot for living things to exist in it. The land above +the water-line was bare rocks. These were rapidly being crumbled by the +action of the air, which was not the mild, pleasant air we know, but was +full of destructive gases, breathed out through cracks in the thin crust +of the earth from the heated mass below. If you stand on the edge of a +lava lake, like one of those on the islands of the Hawaiian group, the +stifling fumes that rise might make you feel as if you were back at the +beginning of the earth's history, when the solid crust was just a thin +film on an unstable sea of molten rock, and this volcano but one of the +vast number of openings by which the boiling lava and the condensed +gases found their way to the surface. Then the rivers ran black with the +waste of the rocky earth they furrowed, and there was no vegetation to +soften the bleakness of the landscape. + +The beginnings of life on the earth are a mystery. Nobody can guess the +riddle. The earliest rocks were subjected to great heat. It is not +possible that life could have existed in the heated ocean or on the +land. Gradually the shores of the seas became filled up with sediment +washed down by the rivers. Layer on layer of this sediment accumulated, +and it was crumpled by pressure, and changed by heat, so that if any +plants or animals had lived along those old shores their remains would +have been utterly destroyed. + +Rocks that lie in layers on top of these oldest, fire-scarred +foundations of the earth show the first faint traces of living things. +Limestone and beds of iron ore are signs of the presence of life. The +first animals and plants lived in the ancient seas. + +From the traces that are left, we judge that the earliest life forms +were of the simplest kind, like some plants and animals that swim in a +drop of water. Have you ever seen a drop of pond water under a compound +microscope? It is a wonder world you look into, and you forget all the +world besides. You are one of the wonderful higher animals, the highest +on the earth. You focus on a shapeless creature that moves about and +feels and breathes, but hasn't any eyes or mouth or stomach--in fact, it +is the lowest form of animal life, and one of the smallest. It is but +one of many animal forms, all simple in structure, but able to feed and +grow and reproduce their kind. + +Gaze out of the window on the garden, now. The flowering plants, the +green grass, and the trees are among the highest forms of plants. In the +drop of water under the microscope tiny specks of green are floating. +They belong to the lowest order of plants. Among the plant and the +animal forms that have been studied and named, are a few living things +the places of which in the scale are not agreed upon. Some say they are +animals; some believe they are plants. They are like both in some +respects. It is probable that the first living things were like these +confusing, minute things--not distinctly plants or animals, but the +parent forms from which, later on, both plants and animals sprang. + +The lowest forms of life, plant and animal, live in water to-day. They +are tiny and their bodies are made of a soft substance like the white of +an egg. If these are at all like the living creatures that swarmed in +the early seas, no wonder they left no traces in the rocks of the early +part of the age when life is first recorded by fossils. Soft-bodied +creatures never do. + +Some of the animals and the plants in the drop of water under the +microscope have body walls of definite shapes, made of lime, or of a +glassy substance called silica. When they die, these "skeletons" lie at +the bottom of the water, and do not decay, as the living part of the +body does, because they are mineral. Gradually a number of these shells, +or hard skeletons, accumulate. In a glass of pond water they are found +at the bottom, amongst the sediment. In a pond how many thousands of +these creatures must live and their shells fall to the bottom at last, +buried in the mud! + +So it is easy to understand why the first creatures on earth left no +trace. The first real fossils found in the rocks are the hard shells or +skeletons of the first plants and animals that had hard parts. + + + + +AN ANCIENT BEACH AT EBB TIDE + + +When the tide is out, the rocks on the Maine coast have plenty of living +creatures to prove this northern shore inhabited. Starfishes lurk in the +hollows, and the tent-shaped shells of the little periwinkle encrust the +wet rocks. Mussels cling to the rocks in clumps, fastened to each other +by their ropes of coarse black hair. The furry coating of sea mosses +that encrust the rocks is a hiding-place for many kinds of living +things, some soft-bodied, some protected by shells. The shallow water is +the home of plants and animals of many different kinds. As proof of this +one finds dead shells and fragments of seaweeds strewn on the shore +after a storm. + +Along the outer shores of the Cape Cod peninsula and down the Jersey +coast, the sober colouring of the shells of the north gives way to a +brighter colour scheme. In the warmer waters, life becomes gayer, if we +may judge by the rich tints that ornament the shells. The kinds of +living creatures change. They are larger and more abundant. The seaweeds +are more varied and more luxuriant in growth. + +When we reach the shores of the West Indian islands and the keys of +Florida the greatest abundance and variety of living forms are found. +The submerged rocks blossom with flower-like sea anemones of every +colour. Corals, branching like trees and bushes on the sea floor, form +groves under water. Among them brilliant-hued fishes swim, and highly +ornamented shells glide, as people know who have gazed through the glass +bottoms of the boats built especially to show visitors the wonderful sea +gardens at Nassau, Bahama Islands, and at Santa Catalina Island, +southern California. + +On every beach the skeletons of animals which die help to build up the +land; though the process is not so rapid in the north as on the shores +that approach the tropics. The coast of Florida has a rim of island +reefs around it built out of coral limestone. Indeed, the peninsula was +built by coral polyps. Houses in St. Augustine are built of coquina +rock, which is simply a mass of broken shells held together by a lime +cement. Every sea beach is packed with shells and other remnants of +animals and plants that live in the shallow waters. Deeper and deeper +year by year the sand buries these skeletons, and many of them are +preserved for all time. + +Thus what is sandy beach to-day may, a few million years from now, be +uncovered as a ledge of sandstone with the prints of waves distinctly +shown, and fossil shells of molluscs, skeletons of fishes, and branches +of seaweed--all of them different from those then growing upon the +earth. + +In the neighbourhood of Cincinnati there have been uncovered banks of +stone accumulated along the border of an ancient sea. From the sides of +granite highlands streams brought down the sand built into these oldest +sandstone rocks. The fine mud which now appears as beds of slate was the +decay of feldspar and hornblende in the same granite. Limestone beds are +full of the fossil shells of creatures that lived in the shallow seas. +Their skeletons, accumulating on the bottom, formed deep layers of +limestone mud. These rocks preserve, by the fossils they contain, a +great variety of shellfish which had limy skeletons. The sea fairly +swarmed along its shallow margin with these creatures. We might not +recognize many of the shells and other curious fossils we find in the +rock uncovered by the workmen who are cutting a railroad embankment. +They are not exactly like the living forms that grow along our beaches +to-day, but they are enough like them for us to know that they lived +along the seashore, and if we had time to examine all the rocks of this +kind preserved in a museum we should decide that seashore life was quite +as abundant then as it is now. The pressed specimens of plants of those +earliest seashores are mere imprints showing that they were pulpy and +therefore gradually decayed. Only their shape is recorded by dark stains +made by each branching part. The decay of the vegetable tissue painted +the outline on the rock which when split apart shows us what those +ancient seaweeds looked like. They belonged to the group of plants we +call kelp, or tangle, which are still common enough in the sea, though +the forms we now have are not exactly like the old ones. Seaweeds belong +to the very lowest forms of plants. + +[Illustration: Crinoid from Indiana] + +[Illustration: _By permission of the American Museum of Natural History_ + +Ammonite from Jurassic of England] + +[Illustration: _By permission of the American Museum of Natural History_ + +Fossil corals Coquina, Hippurite limestone] + +The limestones are full of fossils of corals. Indeed, there must have +been reefs like those that skirt Florida to-day built by these +lime-building polyps. Their forms are so well preserved in the rocks +that it is possible to know just how they looked when they grew in the +shallows. + +One very common kind is called a cup coral, because the polyp formed a +skeleton shaped like a cup. The body wall surrounded the skeleton, and +the arms or tentacles rose from the centre of the funnel-like depression +in the top. Little cups budded off from their parents, but remained +attached, and at length the skeletons of all formed great masses of limy +rock. Some cup corals grew in a solid mass, the new generation forming +an outer layer, thus burying the parent cups. + +A second type of corals in these oldest limestones is the honeycomb +group. The colonies of polyps lived in tubes which lengthened gradually, +forming compact, limy cylinders like organ pipes, fitted close together. +The living generation always inhabited the upper chambers of the tubes. +A third type is the chain coral, made of tubes joined in rows, single +file like pickets of a fence. But these walls bend into curious +patterns, so that the cross-section of a mass of them looks like a +complex pattern of crochet-work, the irregular spaces fenced with chain +stitches. Each open link is a pit in which a polyp lived. + +Among the corals are sprays of a fine feathery growth embedded in the +limestone. Fine, straight, splinter-like branches are saw-toothed on one +or both edges. These limy fossils might not be seen at all, were they +not bedded in shales, which are very fine-grained. Here again are the +skeletons of animals. Each notch on each thread-like branch was the home +of a tiny animal, not unlike a sea anemone and a coral polyp. + +To believe this story it is necessary only to pick up a bit of dead +shell or floating driftwood on which a feathery growth is found. These +plumes, like "sea mosses," as they are called, are not plants at all, +but colonies of polyps. Each one lived in a tiny pit, and these pits +range one above the other, so as to look like notches on the thread-like +divisions of the stem. Put a piece of this so-called "sea moss" in a +glass of sea water, and in a few moments of quiet you will see, by the +use of a magnifying glass, the spreading arms of the polyp thrust out of +each pit. + +The ancient seas swarmed with these living hydrozoans, and their remains +are found preserved as fossils in the shales which once were beds of +soft mud. + +The hard shells of sea urchins and starfishes are made of lime. In the +ancient seas, starfishes were rare and sea urchins did not exist, but +all over the sea bottom grew creatures called crinoids, the soft parts +of which were enclosed in limy protective cases and attached to rocks on +the sea bottom by means of jointed stems. No fossils are more plentiful +in the early limestones than these wonderful "stone lilies." Indeed, the +crinoidal limestone seemed to be built of the skeletons of these +animals. The lily-like body was flung open, as a lily opens its calyx, +when the creature was feeding. But any alarm caused the tentacles to be +drawn in, and the petal-like divisions of the body wall to close tightly +together, till that wall looked like an unopened bud. + +On the bottom of the Atlantic, near the Bahama Islands, these stone +lilies are still found growing. Their jointed stems and body parts are +as graceful in form and motion as any lily. The creature's mouth is in +the centre of the flower-like top, and it feeds like the sea urchin, on +particles obtained in the sea water. + +The old limestones contain great quantities of "lamp shells," which are +old-fashioned bivalves. Their shells remind us of our bivalve clams and +scallops, but the internal parts were very different. The gills of clams +and oysters are soft parts. Inside of the lamp shells are coiled, bony +arms, supporting the fringed gills. + +It is fortunate for us that a few lamp shells still live in the seas. By +studying the soft parts of these living remnants of a very old race we +can know the secrets of the lives of those ancient lamp shells, the +soft parts of which were all washed away, and the fossil shells of which +are preserved. Gradually the lamp shells died out, and the modern +bivalves have come to take their places. Just so, the ancient crinoids +are now almost extinct; the sea urchins and the starfishes have +succeeded them. + +The chambered nautilus has its shell divided by partitions and it lives +in the outer chamber, a many-tentacled creature, that is a close +relative of the soft-bodied squid. In the ancient seas the same family +was represented by huge creatures the shells of which were chambered, +but not coiled. Their abundance and great size are proved by the rocks +in which their fossils are preserved. Some of them must have been the +rulers of the sea, as sharks and whales are to-day. Fossil specimens +have been found more than fifteen feet long and ten inches in diameter +in the ancient rocks of some of the Western States. It is possible to +read from the lowest rock formations upward, the rise of these sea +giants and their gradual decline. Certain strata of limestone contain +the last relics of this race, after which they became extinct. As the +straight-chambered forms diminished, great coiled forms became more +abundant, but all died out. + +One of the most abundant fossil animals in ancient rocks is called a +trilobite. Its body is divided by two grooves into three parts, a +central ridge extending the whole length of the body and two side +ridges. The front portion of the shell formed the head shield, and +behind the main body part was a little tail shield. The skeleton was +formed of many movable jointed plates, and the creature had eyes set in +the head shield just as the king crab's are set. Jointed legs in pairs +fringed each side of the body. Each leg had two branches, one for +walking, the other for swimming. A pair of feelers rose from the head. +The body could be rolled into a ball when danger threatened, by bringing +head and tail together. + +These remarkable, extinct trilobites were the first crustaceans. Their +nearest living relative to-day is the horseshoe crab. The fresh-water +crayfish and the lobster are more distant relatives: so are the shrimps +and the prawns. No such abundance of these creatures exists to-day as +existed when the trilobites thronged the shallows. So well preserved are +these skeletons that, although there are no living trilobites for +comparison, it is possible to find out from the fossil enough about +their structure to know how they fed and lived their lives along with +the straight-horns which were the scavengers of those early seas and the +terror of smaller creatures. The trilobites throve, and, dying, left +their record in the rocks; then disappeared entirely. We find their +fossils in a great variety of forms, shapes, and sizes. The smallest is +but a fraction of an inch long, the largest twenty inches long. + +The ancient rocks, in which these lower forms of life have left their +fossils, are known as the Silurian system. The time in which these rocks +were accumulating under the seas covers a vast period. We call it the +Age of Invertebrates, because these soft-bodied, hard-shelled animals, +the crinoids, the molluscs, and the trilobites, with bony external +skeletons and no backbones, were the most abundant. They overshadowed +all other forms of life. The rocks of this wonderful series were formed +on the shores of a great inland sea that covered the central portion of +North America. In the ages that followed, these rocks were covered +deeply with later sediments. But the upheavals of the crust have broken +open and erosion has uncovered these strata in different regions. +Geologists have found written there, page upon page, the record of life +as it existed in the early seas. + + + + +THE LIME ROCKS + + +"Hard" water and "soft" water are very different. The rain that falls +and fills our cisterns is not softer or more delightful to use than the +well water in some favoured regions. In it, soap makes beautiful, creamy +suds, and it is a real pleasure to put one's hands into it. But in hard +water soap seems to curdle, and some softening agent like borax has to +be added or the water will chap the hands. There is little satisfaction +in using water of this kind for any purpose. + +Hard water was as soft as any when it fell from the sky; but the rain +water trickled into the ground and passed through rocks containing lime. +Some of this mineral was absorbed, for lime is readily soluble in water. +Clear though it may be, water that has lime in it has quite a different +feeling from rain water. Blow the breath into a basin of hard water, and +a milky appearance will be noted. The carbonic acid gas exhaled from the +lungs unites with the invisible lime, causing it to become visible +particles of carbonate of lime, which fall to the bottom of the basin. + +Nearly all well water is hard. So is the water of lakes and rivers and +the ocean, for limestone is one of the most widely distributed rocks in +the surface of the earth. Rain water makes its way into the earth's +crust, absorbs mineral substances, and collects in springs which feed +brooks and rivers and lakes. Wells are holes in the ground which bore +into water-soaked strata of sand. + +We gain something from the lime dissolved in hard water, for it is an +essential part of our food. We must drink a certain amount of water each +day to keep the body in perfect health. The lime in this water goes +chiefly to the building of our bones. Plant roots take up lime in the +water that mounts as sap through the plant bodies. We get some of the +lime we need in vegetable foods we eat. + +All of the kingdom of vertebrate animals, from the lowest forms to the +highest, all of the shell-bearing animals of sea and land, require lime. +Many of the lower creatures especially these in the sea, such as corals +and their near relatives, encase themselves in body walls of lime. They +absorb the lime from the sea water, and deposit it as unconsciously as +we build the bony framework of our bodies. + +All the bone and shell-bearing creatures that die on the earth and in +the sea restore to the land and to the water the lime taken by the +creatures while they lived. Carbonic acid gas in the water greatly +hastens the dissolving of dead shells. Carbonic acid gas, whether free +in the air, or absorbed by percolating water, hastens the dissolving of +skeletons of creatures that die upon land. Then the raw materials are +built again into lime rocks underground. + +The lime rocks are the most important group in the list of rocks that +form the crust of the earth. They are made of the elements calcium, +carbon, and oxygen, yet the different members of this calcite group +differ widely in composition and appearance. So do oyster shells and +beef bones, though both contain quantities of carbonate of lime. + +Calcite is a soft mineral, light in weight, sometimes white, but oftener +of some other colour. It may be found crystallized or not. Whenever a +drop of acid touches it, a frothy effervescence occurs. The drop of acid +boils up and gives off the pungent odour of carbonic acid gas. + +The reason that calcite is hard to find in rocks is that percolating +water, charged with acids, is constantly stealing it, and carrying it +away into the ocean. The rocks that contain it crumble because the limy +portions have been dissolved out. + +Some limestones resist the destructive action of water. When they are +impregnated with silica they become transformed into marble, which takes +a high polish like granite. Acids must be strong to make any impression +on marble. + +The thick beds of pure limestone that underlie the surface soil in +Kentucky and in parts of Virginia sometimes measure several hundred feet +in thickness, a single stratum often being twenty feet thick. They are +all horizontal, for they were formed on sea bottom, and have not been +crumpled in later time. The dead bodies of sea creatures contributed +their shells and skeletons to the lime deposit on the sea bottom. Who +can estimate the time it took to form those thick, solid layers of lime +rock? The animals were corals, crinoids, and molluscs. Little sand and +clay show in the lime rock of this period, before the marshes of the +Carboniferous Age took the place of the ancient inland sea of the +Subcarboniferous Period, the sedimentary accumulations of which we are +now talking about. + +The living corals one sees in the shallow water of the Florida coast +to-day are building land by building up their limy skeletons. The reefs +are the dead skeletons of past generations of these tiny living things. +They take in lime from the water, and use it as we use lime in building +our bones. In each case it is an unconscious process of animal +growth--not a "building process" like a mason's building of a wall. Many +people think that the coral polyp builds in this way. They give it +credit for patience in a great undertaking. All the polyp does is to +feed on whatever the water supplies that its digestive organs can use. +It is like a sea anemone in appearance and in habits of life. It is not +at all like an insect. Yet it is common to hear people speak of the +"coral insect"! Do not let any one ever hear you repeat such a mistake. + +Southern Florida is made out of coral rock, but thinly covered with +soil. It was made by the growth of reef after reef, and it is still +growing. + +The Cretaceous Period of the earth's eventful history is named for the +lime rock which we know as chalk. Beds of this recent kind of limestone +are found in England and in France, pure white, made of the skeletons of +the smallest of lime-consuming creatures, Foraminifera. They swarmed in +deep water, and so did minute sponge animalcules and plant forms called +Diatoms that took silica from the water, and formed their hard parts of +this glassy substance. The result is seen in the nodules of flint found +in the soft, snow-white chalk. Did you ever use a piece of chalk that +scratched the black-board? The flint did it. Have you ever seen the +chalk cliffs of Dover? When you do see them, notice how they gleam white +in the sun. See how the rains have sculptured those cliffs. The +prominences left standing out are strengthened by the flint they +contain. Chalk beds occur in Texas and under our great plains; but the +principal rocks of the age in America were sandstones and clays. + + + + +THE AGE OF FISHES + + +The first animal with a backbone recorded its existence among the +fossils found in rocks of the upper Silurian strata. It is a fish; but +the earliest fossils are very incomplete specimens. We know that these +old-fashioned fishes were somewhat like the sturgeons of our rivers. +Their bodies were encased in bony armour of hard scales, coated with +enamel. The bones of the spine were connected by ball and socket joints, +and the heads were movable. In these two particulars the fishes +resembled reptiles. The modern gar-pike has a number of the same +characteristics. + +Another backboned creature of the ancient seas was the ancestral type of +the shark family. In some points this old-fashioned shark reminds us of +birds and turtles. These early fishes foreshadowed all later +vertebrates, not yet on the earth. After them came the amphibians, then +the reptiles, then the birds, and latest the mammals. + +The race of fishes began, no doubt, with forms so soft-boned that no +fossil traces are preserved in the rocks. When those with harder bones +appeared, the fossil record began, and it tells the story of the passing +of the early, unfish-like forms, and the coming of new kinds, great in +size and in numbers, that swarmed in the seas, and were tyrants over all +other living things. They conquered the giant straight-horns and +trilobites, former rulers of the seas. + +[Illustration: _By permission of the American Museum of Natural History_ + +A sixteen-foot fossil fish from Cretaceous of Kansas, with a modern +tarpon] + +[Illustration: _By permission of the American Museum of Natural History_ + +Canon Diablo meteorite from Arizona] + +One of these giant fishes fifteen to twenty feet long, three feet wide, +had jaws two feet long, set with blade-like teeth. Devonian rocks in +Ohio have yielded fine fossils of gigantic fishes and sharks. + +Devonian fishes were unlike modern kinds in these particulars, the +spinal column extended to the end of the tail, whether the fins were +arranged equally or unequally on the sides; the paired side fins look +like limbs fringed with fins. Every Devonian fish of the gar type seems +to have had a lung to help out its gill-breathing. + +In these traits the first fishes were much like the amphibians. They +were the parent stock from which branched later the true fishes and the +amphibians, as a single trunk parts into two main boughs. The trunk is +the connecting link. + +The sea bottom was still thronged with crinoids, and lamp shells, and +cup corals. Shells of both clam and snail shapes are plentiful. The +chambered straight-horns are fewer and smaller, and coiled forms of this +type of shell are found. Trilobite forms are smaller, and their numbers +decrease. + +The first land plants appeared during this age. Ferns and giant club +mosses and cycads grew in swampy ground. This was the beginning of the +wonderful fern forests that marked the next age, when coal was formed. + +The rocks that bear the record of these living things in their fossils, +form strata of great thickness that overlie the Silurian deposits. There +is no break between them. So we understand that the sea changed its +shore-line only when the Silurian deposits rose to the water-level. + +The Devonian sea was smaller than the Silurian. A great tract of +Devonian deposits occupies the lower half of the state of New York, +Canada between Lakes Erie and Huron, and the northern portions of +Indiana and Illinois. These older layers of the stratified rock are +covered with the deposits of later periods. Rivers that cut deep +channels reveal the earlier rocks as outcrops along their canyon walk. +The record of the age of fishes is, for the most part, still an unopened +book. The pages are sealed, waiting for the geologist with his hammer to +disclose the mysteries. + + + + +KING COAL + + +In this country, and in this age, who can doubt that coal is king? It is +one of the few necessities of life. In various sections of the country, +layers of coal have been discovered--some near the surface, others deep +underground. These are the storehouses of fuel which the coal miners dig +out and bring to the surface, and the railroads distribute. From +Pennsylvania and Ohio to Alabama stretches the richest coal-basin. +Illinois and Indiana contain another. From Iowa southward to Texas +another broad basin lies. Central Michigan and Nova Scotia each has +isolated coal-basins. All these have been discovered and mined, for they +lie in the oldest part of the country. + +In the West, coal-beds have been discovered in several states, but many +regions have not yet been explored. Vast coal-fields, still untouched, +have been located in Alaska. The Government is trying to save this fuel +supply for coming generations. Many of the richest coal-beds from Nova +Scotia southward dip under the ocean. They have been robbed by the +erosive action of waves and running water. Glaciers have ground away +their substance, and given it to the sea. Much that remains intact must +be left by miners on account of the difficulties of getting out coal +from tilted and contorted strata. + +As a rule, the first-formed coal is the best. The Western coal-fields +belong to the period following the Carboniferous Age. Although +conditions were favourable to abundant coal formation, Western coal is +not equal to the older, Eastern coal. It is often called _lignite_, a +word that designates its immaturity compared with anthracite. + +Coal formed in the Triassic Period is found in a basin near Richmond, +Virginia. There is an abundance of this coal, but it has been subjected +to mountain-making pressure and heat, and is extremely inflammable. The +miners are in constant danger on account of coal gas, which becomes +explosive when the air of the shaft reaches and mingles with it. This +the miner calls "fire damp." North Carolina has coal of the same +formation, that is also dangerous to mine, and very awkward to reach, on +account of the crumpling of the strata. + +There are beds of coal so pure that very little ash remains after the +burning. Five per cent, of ash may be reasonably expected in pure coal, +unmixed with sedimentary deposits. Such coal was formed in that part of +the swamp which was not stirred by the inflow of a river. Wherever muddy +water flowed in among the fallen stems of plants, or sand drifted over +the accumulated peat, these deposits remained, to appear later and +bother those who attempt to burn the coal. + +[Illustration: Eocene fish] + +[Illustration: _By permission of the American Museum of Natural History_ + +Trilobite from the Niagara limestone, Upper Silurian, of Western New +York] + +[Illustration: Sigillaria, Stigmaria and Lepidodendron] + +[Illustration: _By permission of the American Museum of Natural History_ + +Coal fern] + +You know pure coal, that burns with great heat and leaves but little +ashes. You know also the other kind, that ignites with difficulty, burns +with little flame, gives out little heat, and dying leaves the furnace +full of ashes. You are trying to burn ancient mud that has but a small +proportion of coal mixed with it. The miners know good coal from poor, +and so do the coal dealers. It is not profitable to mine the impure part +of the vein. It costs as much to mine and ship as the best quality, and +it brings a much lower price. + +The deeper beds of coal are better than those formed in comparatively +recent time and found lying nearer the surface. In many bogs a layer of +embedded root fibres, called peat, is cut into bricks and dried for +burning. Deeper than peat-beds lie the _lignites_, which are old beds of +peat, on the way to become coal. _Soft coal_ is older than lignite. It +contains thirty to fifty per cent. of volatile matter, and burns +readily, with a bright blaze. The richest of this bituminous coal is +called _fat_, or _fusing coal_. The bitumen oozes out, and the coal +cakes in burning. Ordinary soft coal contains less, but still we can see +the resinous bitumen frying out of it as it burns. There is more heat +and less volatile matter in _steam coal_, so-called because it is the +fuel that most quickly forms steam in an engine. _Hard coal_ contains +but five to ten per cent. of volatile matter. It is slow to ignite and +burns with a small blue blaze. + +From peat to anthracite coal I have named the series which increases +gradually in the amount of heat it gives out, and increases and then +decreases in its readiness to burn and in the brightness of its flame. +Anthracite coal has the highest amount of fixed carbon. This is the +reason why it makes the best fuel, for fixed carbon is the substance +which holds the store of imprisoned sunlight, liberated as heat when the +coal burns. Tremendous pressure and heat due to shrinking of the earth's +crust have crumpled and twisted the strata containing coal in eastern +Pennsylvania, and thus changed bituminous coal into anthracite. Ohio +beds, formed at the same time, but undisturbed by heat and pressure, are +bituminous yet. + +The coal-beds of Rhode Island are anthracite, but the coal is so hard +that it will not burn in an open fire. The terrible, mountain-making +forces that crumpled these strata and robbed the coal of its volatile +matter, left so little of the gas-forming element, that a very special +treatment is necessary to make the carbon burn. It is used successfully +in furnaces built for the smelting of ores. + +The last stage in the coal series is a black substance which we know as +black lead, or graphite. We write with it when we use a "lead" pencil. +This is anthracite coal after all of the volatile matter has been driven +out of it. It cannot burn, although it is solid carbon. The beds of +graphite have been formed out of coal by the same changes in the +earth's crust which have converted soft coal into anthracite. + +The tremendous pressure that bears on the coal measures has changed a +part of the carbon into liquid and gaseous form. Lakes of oil have been +tapped from which jets of great force have spouted out. Such +accumulations of oil usually fill porous layers of sandstone and are +confined by overlying and underlying beds of impervious clay. Gas may be +similarly confined until a well is drilled, relieving the pressure, and +furnishing abundant or scanty supply of this valuable fuel. Western +Pennsylvania coal-fields have beds of gas and oil. If mountain-making +forces had broken the strata, as in eastern Pennsylvania, the gas and +the oil would have been lost by evaporation. + +This is what happened in the anthracite coal-belt. + + + + +HOW COAL WAS MADE + + +The broad, rounded dome of a maple tree shades my windows from the +intense heat of this August day. The air is hot, and every leaf of the +tree's thatched roof is spread to catch the sunlight. The carbon in the +air is breathed in through openings on the under side of each leaf. The +sap in the leaf pulp uses the carbon in making starch. The sun's heat is +absorbed. It is the energy that enables the leaf-green to produce a +wonderful chemical change. Out of soil water, brought up from the roots, +and the carbonic acid gas, taken in from the air, rich, sugary starch is +manufactured in the leaf laboratory. + +This plant food returns in a slow current, feeding the growing cells +under the bark, from leaf tip to root tip, throughout the growing tree. +The sap builds solid wood. The maple tree has been built out of muddy +water and carbon gas. It stands a miracle before our eyes. In its tough +wood fibres is locked up all the heat its leaves absorbed from the sun, +since the day the maple seed sprouted and the first pair of leaves +lifted their palms above the ground. + +If my maple tree should die, and fall, and lie undisturbed on the +ground, it would slowly decay. The carbon of its solid frame would pass +back into the air, as gas, and the heat would escape so gradually that I +could not notice it at all, unless I thrust my hand into the warm, +crumbling mass. + +If my tree should be cut down to-day and chopped into stove wood, it +would keep a fire in my grate for many months. + +Burning destroys wood substance a great deal faster than decay in the +open air does, but the processes of rotting and burning are alike in +this: each process releases the carbon, and gives it back to the air. It +gives back also the sun's heat, stored while the tree was growing. There +is left on the ground, and in the ashes on the hearth, only the mineral +substance taken up in the water the roots gathered underground. + +If my tree stood in swampy ground and fell over under a high wind, the +water that covered it and saturated its substance would prevent decay. +The carbon would not be allowed to escape as a gas to the air; the woody +substance would become gradually changed into _peat_. In this form it +might remain for thousands of years, and finally be changed into coal. + +Whether it was burned while yet in the condition of peat, or millions of +years later, when it was transformed into coal, the heat stored in its +substance was liberated by the burning. The carbon and the heat went +back to the air. + +Every green plant we see spreads its leaves to the sun. Every stick of +wood we burn, and every lump of coal, is giving back, in the form of +light and heat, the energy that came from sunshine and was captured by +the green leaves. How long the wood has held this store of heat we may +easily compute, for we can read the age of a tree. But the age of coal +we cannot accurately state. The years probably should be counted by +millions, instead of thousands. + +The great inland sea that covered the middle portion of the continent +during the Silurian and the Devonian periods, became shallow by the +deposit of vast quantities of sediment. Along the lines of the deposits +of greatest thickness, a crumpling of the earth's crust lifted the first +fold of the Alleghany Mountains as a great sea wall on the east, and on +the western shore another formed the beginning of the Ozark Mountain +system in Missouri. An island was lifted out of the sea, forming the +elevated ground on which the city of Cincinnati now stands. Various +other ridges and islands divided the ancient sea into much smaller +bodies of water. Hemmed in by land these shallow sea-basins gradually +changed into fresh-water lakes, for they no longer had connection with +the ocean, and all the water they received came from rain. After +centuries of freshets, and of filling in with the rock debris brought by +the streams, they became great marshes, in which grew water-loving +plants. Generation after generation of these plants died, and their +remains, submerged by the water, were converted into peat. In the +course of ages this peat became coal. This is the history of the coal +measures. + +There is no guesswork here. The stems of plants do not lose their +microscopic structure in all the ages it has taken to transform them to +coal. A thin section of coal shows under a magnifier the structure of +the stems of the coal-forming plants. Moreover, the veins of coal +preserve above or below them, in shales that were once deposits of mud, +the branching trunks of trees, perfectly fossilized. There are no better +proofs of the vegetable origin of coal than the lumps themselves. But +they are plain to the naked eye, while the coal tells its story to the +man with the microscope. + +The fossil remains of the plants that flourished when coal was forming +are gigantic, compared with plants of the same families now living. We +must conclude that the climate was tropical, the air very heavy with +moisture, and charged much more heavily than it is now with carbonic +acid gas. + +These conditions produced, in rapid succession, forests of tree ferns +and horsetails and giant club mosses. These are the three types of +plants out of which the coal was made. They were all rich in resin, +which makes the coal burn readily. The ferns had stems as large as tree +trunks. Some have been found that are eighteen inches in diameter. We +know they are ferns, because the leaves are found with their fruits +attached to them in the manner of present-day ferns. The stems show the +well known scar by which fern leaves are joined. And the wood of these +fossil fern stems is tubular in structure, just as the wood of living +ferns is to-day. + +Among the ferns which dominated these old marsh forests grew one kind, +the scaly leaves of which covered the stems and bore their fruits on the +branching tips. These giants, some of them with trunks four feet in +diameter, belong to the same group of plants as our creeping club +mosses, but in the ancient days they stood up among the other ferns as +trees forty or fifty feet high. + +The giant scouring rushes, or horsetails, had the same general +characteristics as the little reed-like plants we know by those names +to-day. + +The highest plants of the coal period were leafy trees with nut-like +fruits, that resemble the yew trees of the present. These gigantic trees +were the first conifers upon the earth. They foreshadowed the pines and +the other cone-bearing evergreens. Their leaves were broad and their +fruits nut-like. The Japanese ginkgo, or maidenhair fern tree, is an +old-fashioned conifer somewhat like those first examples of this family. +Trunks sixty to seventy feet long, crowned with broad leaves and a spike +of fruit, have been found lying in the upper layers of the coal-seams, +and in sandstone strata that lie between the strata of coal. Peculiar +circular discs, which the microscope reveals along the sides of the wood +fibres of these fossil trees, prove the wood structure to be like that +of modern conifers. + +Generation after generation of forests lived and died in the vast +spreading swamps of this era. The land sank, and freshets came here and +there, drowning out all plant life, and covering the layers of peat with +beds of sand or mud. When the water went down, other forests took +possession, and a new coal-bed was started. It is plainly seen that +flooding often put an end to coal formation. Fifteen seams of coal, one +above another, is the greatest number that have been found. The veins +vary from one inch to forty feet in thickness. These are separated by +layers of sandstone or shale, which accumulated as sediment, covering +the stumps of dead tree ferns and other growths, and preserving them as +fossils to tell the story of those bygone ages as plainly as any other +record could have done. + +Fresh-water animals succeeded those of salt water in the swamps that +formed the coal measures. Overhead, the first insects flitted among the +branches of the tree ferns. Dragon-flies darted above the surface and +dipped in water as they do to-day. Spiders, scorpions, and cockroaches, +all air-breathing insects, were represented, but none of the higher, +nectar-loving insects, like flies and bees and butterflies, were there. +Flowering plants had not yet appeared on the earth. Snakelike +amphibians, some fishlike, some lizard-like, and huge crocodilian forms +appeared for the first time. These air-breathing swamp-dwellers could +not have lived in salt water. + +Fresh-water molluscs and land shells appear for the first time as +fossils in the rocks of the coal measures. On the shores of the ocean, +the rocks of this period show that trilobites, horseshoe crabs, and +fishes still lived in vast numbers, and corals continued to form +limestone. The old types of marine animals changed gradually, but the +coal measures show strikingly different fossils. These rocks bear the +first record of fresh-water and land animals. + + + + +THE MOST USEFUL METAL + + +It is fortunate for us all that, out of the half-dozen so-called useful +metals, iron, which is the most useful of them all to the human race, +should be also the most plentiful and the cheapest. Aluminum is abundant +in the common clay and soil under our feet. But separating it is still +an expensive process; so that this metal is not commercially so +plentiful as iron is, nor is it cheap. + +All we know of the earth's substance is based on studies of the +superficial part of its crust, a mere film compared with the eight +thousand miles of its diameter. Nobody knows what the core of the +earth--the great globe under this surface film--is made of; but we know +that it is of heavier material than the surface layer; and geologists +believe that iron is an important element in the central mass of the +globe. + +One thing that makes this guess seem reasonable is the great abundance +of iron in the earth's crust. Another thing is that meteors which fall +on the earth out of the sky prove to be chiefly composed of iron. All of +their other elements are ones which are found in our own rocks. If we +believe that the earth itself is a fragment of the sun, thrown off in a +heated condition and cooling as it flew through space, we may consider +it a giant meteor, made of the substances we find in the chance meteor +that strikes the earth. + +Iron is found, not only in the soil, but in all plant and animal bodies +that take their food from the soil. The red colour in fruits and +flowers, and in the blood of the higher animals, is a form in which iron +is familiar to us. It does more, perhaps, to make the world beautiful +than any other mineral element known. + +But long before these benefits were understood, iron was the backbone of +civilization. It is so to-day. Iron, transformed by a simple process +into steel, sustains the commercial supremacy of the great civilized +nations of the world. The railroad train, the steel-armoured battleship, +the great bridge, the towering sky-scraper, the keen-edged tool, the +delicate mechanism of watches and a thousand other scientific +instruments--all these things are possible to-day because iron was +discovered and has been put to use. + +It was probably one of the cave men, poking about in his fire among the +rocks, who discovered a lump of molten metal which the heat had +separated from the rest of the rocks. He examined this "clinker" after +it cooled, and it interested him. It was a new discovery. It may have +been he, or possibly his descendants, who learned that this metal could +be pounded into other shapes, and freed by pounding from the pebbles +and other impurities that clung to it when it cooled. The relics of +iron-tipped spears and arrows show the skill and ingenuity of our early +ancestors in making use of iron as a means of killing their prey. The +earliest remains of this kind have probably been lost because the iron +rusted away. + +Man was pretty well along on the road to civilization before he learned +where iron could be found in beds, and how it could be purified for his +use. We now know that certain very minute plants, which live in quiet +water, cause iron brought into that water to be precipitated, and to +accumulate in the bottom of these boggy pools. In ancient days these bog +deposits of iron often alternated with coal layers. Millions of years +have passed since these two useful substances were laid down. To-day the +coal is dug, along with the bog iron. The coal is burned to melt the +iron ore and prepare it for use. It is a fortunate region that produces +both coal and iron. + +Bituminous coal is plentiful, and scattered all over the country, while +anthracite is scarce. The cheapest iron is made in Alabama, which has +its ore in rich deposits in hillsides, and coal measures close by, +furnishing the raw material for coke. The result is that the region of +Birmingham has become the centre of great wealth through the development +of iron and coal mines. + +Where water flows over limestone rock, and percolates through layers of +this very common mineral, it causes the iron, gathered in these rock +masses, to be deposited in pockets. All along the Appalachian Mountains +the iron has been gathered in beds which are being mined. These beds of +ore are usually mixed with clay and other earthy substances from which +the metal can be separated only by melting. The ore is thrown into a +furnace where the metal melts and trickles down, leaving behind the +non-metallic impurities. It is drawn off and run into moulds, where it +cools in the form of "pig" iron. + +The first fuel used in the making of pig iron from the ore was charcoal. +In America the early settlers had no difficulty in finding plenty of +wood. Indeed, the forests were weeds that had to be cut down and burned +to make room for fields of grain. The finding of iron ore always started +a small industry in a colony. If there was a blacksmith, or any one else +among the small company who understood working in iron, he was put in +charge. + +To make the charcoal, wood was cut and piled closely in a dome-shaped +heap, which was tightly covered with sods, except for a small opening +near the ground. In this a fire was built, and smothered, but kept going +until all the wood within the oven was charred. + +This fuel burned readily, with an intense heat, and without ashes. +Sticks of charcoal have the form of the wood, and they are stiff enough +to hold up the ore of iron so that it cannot crush out the fire. For a +long time American iron was supplied by little smelters, scattered here +and there. The workmen beat the melted metal on the forge, freeing it +from impurities, and shaping the pure metal into useful articles. +Sometimes they made it into steel, by a process learned in the Old +World. + +The American iron industry, which now is one of the greatest in the +world, centres in Pittsburg, near which great deposits of iron and coal +lie close together. The making of coke from coal has replaced the +burning of charcoal for fuel. When the forests were cut away by +lumbermen, the supply of charcoal threatened to give out, and +experiments were made in charring coal, which resulted in the successful +making of coke, a fuel made from coal by a process similar to the making +of charcoal from wood. The story of the making of coke out of hard and +soft coal is a long one, for it began as far back as the beginning of +the nineteenth century. + +In 1812 the first boat-load of anthracite coal was sent to Philadelphia +from a little settlement along the Lehigh River. A mine had been opened, +the owner of which believed that the black, shiny "rocks" would burn. +His neighbours laughed at him, for they had tried building fires with +them, and concluded that it could not be done. In Philadelphia, the +owners of some coke furnaces gave the new fuel a trial, in spite of the +disgust of the stokers, who thought they were putting out their fires +with a pile of stones. After a little, however, the new fuel began to +burn with the peculiar pale flame and intense heat that we know so +well, and the stokers were convinced that here was a new fuel, with +possibilities in it. + +But it was hard for people to be patient with the slow starting of this +hard coal. Not until 1840 did it come into general favour, following the +discovery that if hot air was supplied at the draught, instead of cold, +anthracite coal became a perfect fuel. + +At Connellsville, Pennsylvania, a vein of coal was discovered which made +coke of the very finest quality. Around this remarkable centre, coke +ovens were built, and iron ore was shipped in, even from the rich beds +of the Lake Superior country. But it was plain to see that Connellsville +coal would become exhausted; and so experiments in coke-making from +other coals were still made. When soft coal burns, a waxy tar oozes out +of it, which tends to smother the fire. Early experiments with coal in +melting iron ore indicated that soft coal was useless as a substitute +for charcoal and coke; but later experiments proved that coke of fine +quality can be made out of this bituminous soft coal, by drawing off the +tar which makes the trouble. New processes were invented by which +valuable gas and coal tar are taken out of bituminous coal, leaving, as +a residue, coke that is equal in quality to that made from the +Connellsville coal. Fortunes have been made out of the separation of the +elements of the once despised soft coal. For the coke and each of its +by-products, coal tar and coal gas, are commercial necessities of life. + +The impurities absorbed by the melting iron ore include carbon, +phosphorus, and silicon. Carbon is the chief cause of the brittleness of +cast iron. The puddling furnace was invented to remove this trouble. The +melted ore was stirred on a broad, basin-like hearth, with a +long-handled puddling rake. The flames swept over the surface, burning +the carbon liberated by the stirring. It was a hard, hot job for the man +at the rake, but it produced forge iron, that could be shaped, hot or +cold, on the anvil. + +The next improvement was the process of pressing the hot iron between +grooved rollers to rid it of slag and other foreign matters collected in +the furnace. The old way was to hammer the metal free from such +impurities. This was slow and hard work. + +Iron was an expensive and scarce metal until the hot blast-furnace +cheapened the process of smelting the ore. The puddling furnace and the +grooved rollers did still more to bring it into general use. The +railroads developed with the iron industry. Soon they required a metal +stronger than iron. Steel was far too expensive, though it was just what +was needed. Efforts were made to find a cheap way to change iron into +steel. Sir Henry Bessemer solved the problem by inventing the Bessemer +converter. It is a great closed retort, which is filled with melted pig +iron. A draught admits air, and the carbon is all burned out. Then a +definite amount of carbon, just the amount required to change iron into +steel, is added, by throwing in bars of an alloy of carbon and +manganese. The latter gives steel its toughness, and enables it to +resist greater heat without crystallizing and thus losing its temper. + +When the carbon has been put in, the retort is closed. The molten metal +absorbs the alloy, and the product is Bessemer steel. In fifteen minutes +pig iron can be transformed into ingot steel. The invention made +possible the use of steel in the construction of bridges, high +buildings, and ships. It made this age of the world the Age of Steel. + + + + +THE AGE OF REPTILES + + +Two big and interesting reptiles we see in the Zoo, the crocodile and +its cousin, the alligator. In the everglades of Florida both are found. +The crocodile of the Nile is protected by popular superstition, so it is +in better luck than ours. The alligators have been killed off for their +skins, and it is only a matter of time till these lumbering creatures +will be found only in places where they are protected as the remnants of +a vanished race. Giant reptiles of other kinds are few upon the earth +now. The _boa constrictor_ is the giant among snakes. The great tropical +turtles represent an allied group. Most of the turtles, lizards, and +snakes are small, and in no sense dominant over other creatures. + +The rocks that lie among the coal measures contain fossils of huge +animals that lived in fresh water and on land, the ancestors of our +frogs, toads, and salamanders, a group we call amphibians. Some of these +animals had the form of snakes; some were fishlike, with scaly bodies; +others were lizard-like or like huge crocodiles. These were the +ancestors of the reptiles, which became the rulers of land and sea +during the Mesozoic Era. The rocks that overlie the coal measures +contain fossils of these gigantic animals. + +Strange crocodile-like reptiles, with turtle-like beaks and tusks, but +no teeth, left their skeletons in the mud of the shores they frequented. +And others had teeth in groups--grinders, tearers, and cutters--like +mammals. These had other traits like the old-fashioned, egg-laying +mammals, the duck-billed platypus, for example, that is still found in +Australia. Along with the remains of these creatures are found small +pouched mammals, of the kangaroo kind, in the rocks of Europe and +America. These land animals saw squatty cycads, and cone-bearing trees, +the ancestors of our evergreens, growing in forests, and marshes covered +with luxuriant growths of tree ferns and horsetails, the fallen bodies +of which formed the recent coal that is now dug in Virginia and North +Carolina. Ammonites, giant sea snails, with chambered shells that +reached a yard and more in diameter, and gigantic squids, swam the seas. +Sea urchins, starfish, and oysters were abundant. Insects flitted +through the air, but no birds appeared among the trees or beasts in the +jungles. Over all forms of living creatures reptiles ruled. They were +remarkable in size and numbers. There were swimming, running, and flying +forms. + +[Illustration: Banded sandstone from Calico Canon, South Dakota] + +[Illustration: _By permission of the American Museum of Natural History_ + +Opalized wood from Utah] + +[Illustration: _By permission of the American Museum of Natural History_ + +Restoration of a carnivorous Dinosaur, Allosaurus, from the Upper +Jurassic and Lower Cretaceous of Wyoming. When erect the animal was +about 15 feet high] + +The fish-reptile, _Ichthyosaurus_, was a hump-backed creature, thirty to +forty feet long, with short neck, very large head, and long jaw, set +with hundreds of pointed teeth. Its eye sockets were a foot across. The +four short limbs were strong paddles, used for swimming. The long, +slender tail ended in a flat fin. Perfect skeletons of this creature +have been found. Its rival in the sea was the lizard-like +_Plesiosaurus_, the small head of which was mounted on a long neck. The +tail was short, but the paddles were long and powerful. No doubt this +agile creature held its own, though somewhat smaller than the more +massively built Ichthyosaurus. + +The land reptiles called _Dinosaurs_ were the largest creatures that +have ever walked the earth. In the American Museum of Natural History, +in New York, the mounted skeleton of the giant Dinosaur fairly takes +one's breath away. It is sixty-six feet long, and correspondingly large +in every part, except its head. This massive creature was remarkably +short of brains. + +The strangest thing about the land reptiles is the fact that certain of +them walked on their hind legs, like birds, and made three-toed tracks +in the mud. Indeed, these fossil tracks, found in slate, were called +bird tracks, until the bones of the reptile skeleton with the bird-like +foot were discovered. Certain long grooves in the slate, hitherto +unexplained, were made by the long tail that dragged in the mud. + +When the mud dried, and was later covered with sediment of another kind, +these prints were preserved, and when the bed of rock was discovered by +quarrymen, the two kinds split apart, showing the record of the stroll +of a giant along the river bank in bygone days. + +The flying reptiles were still more bird-like in structure, though +gigantic in size. Imagine the appearance of a great lizard with +bat-like, webbed wings and bat-like, toothed jaws! The first feathered +fossil bird was discovered in the limestone rock of Bavaria. It was a +wonderfully preserved fossil, showing the feathers perfectly. Three +fingers of each "hand" were free and clawed, so that the creature could +seize its prey, and yet use its feathered wings in flight. The small +head had jaws set with socketed teeth, like a reptile's, and the long, +lizard tail of twenty-one bones had a pair of side feathers at each +joint. This _Archeopteryx_ is the reptilian ancestor of birds. During +this age of the world, one branch of the reptile group established the +family line of birds. The bird-like reptiles are the connecting link +between the two races. How much both birds and reptiles have changed +from that ancient type, their common ancestor! + +I have mentioned but a few of the types of animals that make the +reptilian age the wonder of all time. One after another skeletons are +unearthed and new species are found. The Connecticut River Valley, with +its red sandstones and shales of the Mesozoic Era, is famous among +geologists, because it preserves the tracks of reptiles, insects, and +crustaceans. These signs tell much of the life that existed when these +flakes of stone were sandy and muddy stretches Not many bones have been +found, however. The thickness of these rocks is between one and two +miles. The time required to accumulate so much sediment must have been +very great. + +[Illustration: _By permission of the American Museum of Natural History_ + +Model of a three-horned Dinosaur, _Triceratops_, from Cretaceous of +Montana. Animal in life about 25 feet long] + +[Illustration: _By permission of the American Museum of Natural History_ + +Mounting the forelegs of _Brontosaurus_, the aquatic Dinosaur] + +It is not clear just what caused the race of giant reptiles to decline +and pass away. The climate did not materially change. Perhaps races grow +old, and ripe for death, after living long on the earth. It seems as if +their time was up; and the clumsy giants abdicated their reign, leaving +dominion over the sea, the air, and the land to those animals adapted to +take the places they were obliged to vacate. + + + + +THE AGE OF MAMMALS + + +The warm-blooded birds and mammals followed the reptiles. This does not +mean that all reptiles died, after having ruled the earth for thousands +of years. It means that changes in climate and other life conditions +were unfavourable to the giants of the cold-blooded races, and gradually +they passed away. They are represented now on the earth by lesser +reptiles, which live comfortably with the wild creatures of other +tribes, but which in no sense rule in the brute creation. They live +rather a lurking, cautious life, and have to hide from enemies, except a +few more able kinds, provided with means of defense. + +There were mammals on the earth in the days of reptilian supremacy, but +they were small in size and numbers, and had to avoid any open conflict +with the giant reptiles, or be worsted in a fight. Now the time came +when the ruling power changed hands. The mammals had their turn at +ruling the lower animals. It was the beginning of things as they are +to-day, for mammals still rule. But many millions of years have probably +stood between the age when this group of animals first began to swarm +over the earth, and the time when Man came to be ruler over all created +things. + +Among the reptiles of the period when the sea, the land, and the air +were swarming with these great creatures were certain kinds that had +traits of mammals. Others were bird-like. From these reptilian ancestors +birds and mammals have sprung. No one doubts this. The fossils prove it, +step by step. + +Yet the rocks surprise the geologist with the suddenness with which many +new kinds of mammals appeared on the earth. Possibly the rocks +containing the bones of so many kinds were fortunately located. The +spots may have been morasses where migrating mammals were overwhelmed +while passing. Possibly conditions favored the rapid development of new +kinds, and the multiplication of their numbers. Warm, moist climate +furnished abundant succulent plant food for the herbivors, and these in +turn furnished prey for the carnivors. + +The coal formed during the Tertiary Period gives added proof that the +plant life was luxuriant. The kinds of trees that grew far north of our +present warm zones have left in the rocks evidence in the form of +perfect leaves and cones and other fruits. For instance, magnolias grew +in Greenland, and palm trees in Dakota. The temperature of Greenland was +thirty degrees warmer than it is now. Our Northern States lie in a belt +that must have had a climate much like that of Florida now. Europe was +correspondingly mild. + +A special chapter tells of the gradual development of the horse. One +hundred different kinds of mammals have been found in the Eocene rocks, +many of which have representative species at the same time in Europe and +America. The rocks of Asia probably have similar records. + +The Eocene rocks, lowest of the Tertiary strata, contain remains of +animals the families of which are now extinct. Next overlying the +Eocene, the Miocene rocks have fossils of animals belonging to modern +families--rhinoceroses, camels, deer, dogs, cats, horses--but the genera +of which are now extinct. The Pliocene strata (above the Miocene) +contains fossils of animals so closely related to the wild animals now +on the earth as to belong to the same genera. They differ from modern +kinds only in the species, as the red squirrel is a different species +from the gray. + +So the record in the rocks shows a gradual approach of the mammals to +the kinds we know, a gradual passing of the mighty forms that ruled by +size and strength, and the coming of forms with greater intelligence, +adapted to the change to a colder climate. + +It sometimes happens that a farmer, digging a well on the prairie, +strikes the skeleton of a monster mammal, called the _mastodon_. This +very thing happened on a neighbour's farm when I was a girl, in Iowa. +Everybody was excited. The owner of the land dug out every bone, careful +that the whole skeleton be found. As he expected, the director of a +museum was glad to pay a high price for the bones. + +[Illustration: _By permission of the American Museum of Natural History_ + +Restoration of an aquatic Dinosaur, _Brontosaurus excelsus_, from the +Upper Jurassic and Lower Cretaceous of Wyoming. The animal in life was +over 60 feet long] + +[Illustration: _By permission of the American Museum of Natural History_ + +Restoration of the small carnivorous Dinosaur, _Ornitholestes hermanui_, +catching a primitive bird _Archaeopteryx_. Upper Jurassic and Lower +Cretaceous] + +The mastodon was about the size of an elephant, with massive limbs, and +large, heavy head that bore two stout, up-curved tusks of ivory. The +creature moved in herds like the buffalo from swamp to swamp; and old +age coming on, the individual, unable to keep up with the herd, sank to +his death in the boggy ground. The peat accumulated over his bones, +undisturbed until thousands of years elapse, and the chance digging of a +well discovers his skeleton. + +Frozen in the ice of northern Siberia, near the mouths of rivers, a +number of mammoths have been found. These are creatures of the elephant +family, and belonging to the extinct race that lived in the Quaternary +Period, just succeeding the Tertiary. The ice overtook the specimens, +and they have been in cold storage ever since. For this reason, both +flesh and bones are preserved, a rare thing to happen, and rarer still +to be seen by a scientist. + +The ignorant natives made a business of watching the ice masses at the +river mouth for dark spots that showed where a mammoth was encased in +the ice. If an iceberg broke off near such a place, the sun might thaw +the ice front of the glacier, until the hairy monster could at length be +reached. His long hair served for many uses, and the wool that grew +under the hair was used as a protection from the Arctic winter. The +frozen flesh was eaten; the bones carved into useful tools; but the +chief value of the find was in the great tusks of ivory, that curved +forward and pointed over the huge shoulders. It was worth a fortune to +get a pair and sell them to a buyer from St. Petersburg. + +One of the finest museum specimens of the mammoth was secured by buying +the tusks of the dealer, and by his aid tracing the location of the +carcass, which was found still intact, except that dogs had eaten away +part of one foreleg, bone and all. From this carefully preserved +specimen, models have been made, exactly copying the shape and the size +of the animal, its skin, hair, and other details. + +The sabre-toothed tiger, the sharp tusks of which, six to eight inches +long, made it a far more ferocious beast than any modern tiger of +tropical jungles, was a Quaternary inhabitant of Europe and America. So +was a smaller tiger, and a lion. The Irish elk, which stood eleven feet +high, with antlers that spread ten feet apart at the tips, was monarch +in the deer family, which had several different species on both +continents. Wild horses and wild cattle, one or two of great size, +roamed the woods, while rhinos and the hippopotamus kept near the +water-courses. Hyenas skulked in the shadows, and acted as scavengers +where the great beasts of prey had feasted. Sloths and cuirassed +animals, like giant armadillos, lived in America. Among bears was one, +the cave bear, larger than the grizzly. True monkeys climbed the trees. +Flamingo, parrots, and tall secretary birds followed the giant +_gastornis_, the ancestor of wading birds and ostriches, which stood ten +feet high, but had wings as small and useless as the auk of later times. + +With the entrance of the modern types of trees, came other flowering +plants, and with them the insects that live on the nectar of flowers. +Through a long line of primitive forms, now extinct, flowering plants +and their insect friends conform to modern types. The record is written +in the great stone book. + +The Age of Mammals in America and Europe ended with the gradual rise of +the continental areas, and a fall of temperature that ushered in the Ice +Age. With the death of tropical vegetation, the giant mammals passed +away. + + + + +THE HORSE AND HIS ANCESTORS + + +Every city has a horse market, where you may look over hundreds of +animals and select one of any colour, size, or kind. The least in size +and weight is the Shetland pony, which one man buys for his children to +drive or ride. Another man wants a long-legged, deep-chested hunter. +Another wants heavy draught-horses, with legs like great pillars under +them, and thick, muscular necks--horses weighing nearly a ton apiece and +able to draw the heaviest trucks. What a contrast between these slow but +powerful animals and the graceful, prancing racer with legs like +pipe-stems--fleet and agile, but not strong enough to draw a heavy load! + +All these different breeds of horses have been developed since man +succeeded in capturing the wild horse and making it help him. Man +himself was still a savage, and he had to fight with wild beasts, as if +he were one of them, until he discovered that he could conquer them by +some power higher than physical strength. From this point on, human +intelligence has been the power that rules the lower animals. Its +gradual development is the story of the advance of civilization on the +earth. Through unknown thousands of years it has gone on, and it is not +yet finished. + +[Illustration: _By permission of the American Museum of Natural History_ + +Restoration of a Siberian mammoth, _Elephas primogenius_, pursued by men +of the old stone age of Europe. Late Pleistocene epoch] + +[Illustration: _By permission of the American Museum of Natural History_ + +Restoration of a small four-toed ancestor of the horse family, _Eohippus +venticolus_. Lower Eocene of Wyoming] + +Just when and where and how our savage ancestors succeeded in taming the +wild horse of the plains and the forests of Europe or Asia is unknown. +Man first made friends with the wild sheep, which were probably more +docile than wild oxen and horses. We can imagine cold and hungry men +seeking shelter from storms in rocky hollows, where sheep were huddled. +How warm the woolly coats of these animals felt to their human +fellow-creatures crowded in with them in the dark! + +It is believed that the primitive men who used stone axes as implements +and weapons, learned to use horses to aid them in their hunting, and in +their warfare with beasts and other men. Gradually these useful animals +were adapted to different uses; and at length different breeds were +evolved. Climate and food supply had much to do with the size and the +character of the breeds. In the Shetland Islands the animals are +naturally dwarfed by the cold, bleak winters, and the scant vegetation +on which they subsist. In middle Europe, where the summers are long and +the winters mild, vegetation is luxurious, and the early horses +developed large frames and heavy muscles. The Shetland pony and the +Percheron draught-horse are the two extremes of size. + +What man has done in changing the types of horses is to emphasize +natural differences. The offspring of the early heavy horses became +heavier than their parents. The present draught-horse was produced, +after many generations, all of which gradually approached the type +desired. The slender racehorses, bred for speed and endurance rather +than strength, are the offspring of generations of parents that had +these qualities strongly marked. Hence came the English thoroughbred and +the American trotter. + +We can read in books the history of breeds of horses. Our knowledge of +what horses were like in prehistoric times is scant. It is written in +layers of rock that are not very deep, but are uncovered only here and +there, and only now and then seen by eyes that can read the story told +by fossil skeletons of horses of the ages long past. + +Geologists have unearthed from time to time skeletons of horses. It was +Professor Marsh who spent so much time in studying the wonderful beds of +fossil mammals in the western part of this country, and found among them +the skeletons of many species of horses that lived here with camels and +elephants and rhinoceroses and tigers, long before the time of man's +coming. + +How can any one know that these bones belonged to a horse's skeleton? +Because some of them are like the bones of a modern horse. It is an easy +matter for a student of animal anatomy to distinguish a horse from a cow +by its bones. The teeth and the foot are enough. These are important and +distinguishing characters. It is by peculiarities in the formation of +the bones of the foot that the different species of extinct horses are +recognized by geologists. + +Wild horses still exist in the wilds of Russia. Remains of the same +species have been dug out of the soil and found in caves in rocky +regions. Deeper in the earth are found the bones of horses differing +from those now living. The bones of the foot indicate a different kind +of horse--an unknown species. But in the main features, the skeleton is +distinctly horse-like. + +In rocks of deeper strata the fossil bones of other horses are found. +They differ somewhat from those found in rocks nearer the surface of the +earth, and still more from those of the modern horse. The older the +rocks, the more the fossil horse differs from the modern. Could you +think of a more interesting adventure than to find the oldest rocks that +show the skeletons of horses? + +The foot of a horse is a long one, though we think of it as merely the +part he walks on. A horse walks on the end of his one toe. The nail of +the toe we call the "hoof." The true heel is the hock, a sharp joint +like an elbow nearly half way up the leg. Along each side of the cannon, +the long bone of this foot, lies a splint of bone, which is the remnant +of a toe, that is gradually being obliterated from the skeleton. These +two splints in the modern horse's foot tell the last chapter of an +interesting story. The earliest American horse, the existence of which +is proved by fossil bones, tells the first chapter. The story has been +read backward by geologists. It is told by a series of skeletons, found +in successive strata of rock. + +The "Bad Lands" of the arid Western States are rich in fossil remains of +horses. Below the surface soil lie the rocks of the Quaternary Period, +which included the drift laid down by the receding glaciers and the +floods that followed the melting of the ice-sheet. Under the Quaternary +lie the Tertiary rocks. These comprise three series, called the Eocene, +Miocene, and Pliocene, the Eocene being the oldest. In the middle region +of North America, ponds and marshy tracts were filled in during the +Tertiary Period, by sediment from rivers; and in these beds of clay and +other rock debris the remains of fresh-water and land animals are +preserved. Raised out of water, and exposed to erosive action of wind +and water, these deposits are easily worn away, for they have not the +solidity of older rocks. They are the crumbly Bad Lands of the West, cut +through by rivers, and strangely sculptured by wind and rain. Here the +fossil horses have been found. + +_Eohippus_, the dawn horse, is the name given a skeleton found in 1880 +in the lower Eocene strata in Wyoming. This specimen lay buried in a +rock formation ages older than that in which the oldest known skeleton +of this family had been found. Its discovery made a great sensation +among scientists. This little animal, the skeleton of which is no larger +than that of a fox, had four perfect toes, and a fifth splint on the +forefoot, and three toes on the hind foot. The teeth are herbivorous. + +_Orohippus_, with a larger skeleton, was found in the middle Eocene +strata of Wyoming. Its feet are like those of its predecessor, except +that the splint is gone. The teeth as well as the feet are more like +those of the modern horse. + +_Mesohippus_, the three-toed horse, found in the Miocene, shows the +fourth toe reduced to splints, and the skeleton as big as that of a +sheep. In this the horse family becomes fairly established. + +_Hypohippus_, the three-toed forest horse, found in the middle Miocene +strata of Colorado, is a related species, but not a direct ancestor of +the modern horse. + +_Neohipparion_, the three-toed desert horse, from the upper Miocene +strata, shows the three toes still present. But the Pliocene rocks +contain fossils showing gradual reduction of the two side toes, +modification of the teeth, and increase in size of the skeleton. + +_Protohippus_ and _Pliohippus_, the one-toed species from the Pliocene +strata, illustrate these changes. They were about the size of small +ponies. + +_Equus_, the modern horse, was represented in the Pliocene strata by a +species, now extinct, called _Equus Scotti_. This we may regard as the +true wild horse of America, for it was as large as the domesticated +horse, and much like it, though more like a zebra in some respects. No +one can tell why these animals, once abundant in this country, became +extinct at the end of the Tertiary Period. But this is undoubtedly true. + +The types described form a series showing how the ancestors of the +modern horse, grazing on the marshy borders of ancient ponds, lived and +died, generation after generation, through a period covering thousands, +possibly millions, of years. Along the sides of the crumbling buttes +these ancient burying-grounds are being uncovered. Within a dozen years +several expeditions, fitted out by the American Museum of Natural +History, have searched the out-cropping strata in Dakota and Wyoming for +bones of mammals known to have lived at the time the strata were forming +in the muddy shallows along the margins of lake and marsh. Duplicate +skeletons of the primitive horse types above have been found, and vast +numbers of their scattered bones. Each summer geological excursions will +add to the wealth of fossils of this family collected in museums. + +The Tertiary rocks in Europe yield the same kind of secrets. The region +of Paris overlies the estuary of an ancient river. When the strata are +laid bare by the digging of foundations for buildings, bones are found +in abundance. Cuvier was a famous French geologist who made extensive +studies of the remains of the prehistoric animals found in this old +burial-place called by scientists the Paris basin. He believed that the +dead bodies floated down-stream and accumulated in the mud of the +delta, where the tide checked the river's current. + +Skeletons of the Hipparion, a graceful, three-toed horse, were found in +numbers in the strata of the Miocene time. This animal lived in Europe +while the Pliohippus and the Protohippus were flourishing in America. + +A great number of species of tapir-like animals left their bones in the +Paris basin, among them a three-hoofed animal which may have been the +connecting link between the horse and the tapir families. Cuvier found +the connecting link between tapirs and cud-chewing mammals. + + + + +THE AGE OF MAN + + +The hairy, woolly mammoth was one of the giant mammals that withstood +the cold of the great ice flood, when the less hardy kinds were cut off +by the changing climate of the northern half of Europe and America. In +caves where the wild animals took refuge from their enemies, skeletons +of men have been found with those of the beasts. With these chance +skeletons have been found rude, chipped stone spear-heads, hammers, and +other tools. With these the savage ancestors of our race defended +themselves, and preyed on such animals as they could use for food. They +hunted the clumsy mammoth successfully, and shared the caverns in the +rocks with animals like the hyena, the sabre-toothed tiger, and the cave +bear, which made these places their homes. In California a human skull +was found in the bed of an ancient river, which was buried by a lava +flow from craters long ago extinct. With this buried skull a few +well-shaped but rough stone tools were found. This man must have lived +when the great ice flood was at its height. + +In southern France, caves have been opened that contained bones and +implements of men who evidently lived by fishing and hunting. Bone +fish-hooks showed skill in carving with the sharp edges of flint +flakes. A spirited drawing of a mammoth, made on a flat, stone surface, +is a proof that savage instincts were less prominent in these cave men +than in those who fought the great reindeer and the mammoth farther +north. + +In later times men of higher intelligence formed tribes, tamed the wild +horse, the ox, and the sheep, and made friends with the dog. Great heaps +of shells along the shores show where the tribes assembled at certain +times to feast on oysters and clams. Bones of animals used as food, and +tools, are found in these heaps, called "kitchen-middens." These are +especially numerous in Northern Europe. The stone implements used by +these tribes were smoothly polished. A higher intelligence expressed +itself also by the making of utensils out of clay. This pottery has been +found in shell heaps. So the rude cave man, who was scarcely less a wild +beast than the animals which competed with him for a living and a +shelter from storms and cold, was succeeded by a higher man who brought +the brutes into subjection by force of will and not by physical +strength. + +The lake-dwellers, men of the Bronze Age, built houses on piles in the +lakes of Central Europe. About sixty years ago the water was low, and +these relics of a vanished race were first discovered. The lake bottoms +were scraped for further evidences of their life. Tools of polished +stone and of bronze were taken up in considerable numbers. Stored +grains and dried fruits of several kinds were found. Ornamental +trinkets, weapons of hunters and warriors, and agricultural tools tell +how the people lived. Their houses were probably built over the water as +a means of safety from attack of beasts or hostile men. + +In our country the mound-builders have left the story of their manners +of life in the spacious, many-roomed tribal houses, built underground, +and left with a great variety of relics to the explorers of modern +times. These people worked the copper mines, and hammered and polished +lumps of pure metal into implements for many uses. With these are tools +of polished stone. Stores of corn were found in many mounds scattered in +the Mississippi Valley. + +The cliff-dwellers of the mesas of Arizona and New Mexico had habits +like those of the mound-builders, and the Aztecs, a vanished race in the +Southwest, at whose wealth and high civilization the invading Spaniards +under Cortez marvelled. The plastered stone houses of the cliff-dwelling +Indians had many stories and rooms, each built to house a tribe, not +merely a family. + +The Pueblo, the Moqui, and the Zuni Indians build similar dwellings +to-day, isolated on the tops of almost inaccessible mesas. + +Millions of years have passed since life appeared on the earth. +Gradually higher forms have followed lower ones in the sea and on the +land. But not all of the lower forms have gone. All grades of plants +and animals still flourish, but the dominant class in each age is more +highly organized than the class that ruled the preceding age. + +To discover the earth's treasure, and to turn it to use; to tame wild +animals and wild plants, and make them serve him; to create ever more +beautiful and more useful forms in domestication; to find out the +earth's life story, by reading the pages of the great stone book--these +are undertakings that waited for man's coming. + + * * * * * + + + + +PART II + +THE SKY + + * * * * * + + + + +EVERY FAMILY A "STAR CLUB" + + +The best family hobby we have ever had is the stars. We have a star club +with no dues to pay, no officers to boss us, and only three rules: + +1. We shall have nothing but "fun" in this club--no hard work. Therefore +no mathematics for us! + +2. We can't afford a telescope. Therefore we must be satisfied with what +bright eyes can see. + +3. No second-hand wonders for us! We want to see the things ourselves, +instead of depending on books. + +You can't imagine what pleasure we have had in one short year! The baby, +of course, was too young to learn anything, and besides he was in bed +long before the stars came out. But Ruth, our seven-year-old, knows ten +of the fifteen brightest stars; and she can pick out twelve of the most +beautiful groups or constellations. We grown-ups know all of the +brightest stars, and all forty-eight of the most famous constellations. +And the whole time we have given to it would not exceed ten minutes a +day! + +And the best part is the _way_ we know the stars. The sky is no longer +bewildering to us. The stars are not cold, strange, mysterious. They are +friends. We know their faces just as easily as you know your playmates. +For instance, we know Sirius, because he is the brightest. We know +Castor and Pollux, because they are twins. We know Regulus, because he +is in the handle of the Sickle. And some we know by their colours. They +are just as different as President Taft, "Ty" Cobb, Horace Fletcher and +Maude Adams. And quite as interesting! + +What's more, none of us can ever get lost again. No matter what strange +woods or city we go to, we never get "turned around." Or if we do, we +quickly find the right way by means of the sun or the stars. + +Then, too, our star club gives us all a little exercise when we need it +most. Winter is the time when we all work hardest and have the fewest +outdoor games. Winter is also the best time for young children to enjoy +the stars, because it gets dark earlier in winter--by five o'clock, or +long before children go to bed. It is pleasant to go out doors for half +an hour before supper and learn one new star or constellation. + +Again, it is always entertaining because every night you find the old +friends in new places. No two nights are just the same. The changes of +the moon make a great difference. Some nights you enjoy the moonlight; +other nights you wish there were no moon, because it keeps you from +spying out some new star. We have a little magazine that tells us all +the news of the stars and the planets and the comets _before_ the things +happen! We pay a dollar a year for it. It is called the _Monthly +Evening Sky Map_. + +When we first became enthusiastic about stars, the father of our family +said: "Well, I think our Star Club will last about two years. I judge it +will cost us about two dollars and we shall get about twenty dollars +worth of fun out of it." But in all three respects father was mistaken. + +Part of the two dollars father spoke of went for a book called "The +Friendly Stars," and seventy-five cents we spent for the most +entertaining thing our family ever bought--a planisphere. This is a +device which enables us to tell just where any star is, at any time, day +or night, the whole year. It has a disc which revolves. All we have to +do is to move it until the month and the day come right opposite the +very hour we are looking at it, and then we can tell in a moment which +stars can be seen at that time. Then we go down the street where there +is a good electric light at the corner and we hold our planisphere up, +almost straight overhead. The light shines through, so that we can read +it, and it is just as if we had a map of the heavens. We can pick out +all the interesting constellations and name them just as easily as we +could find the Great Lakes or Rocky Mountains in our geography. + +We became so eager not to miss any good thing that father got another +book. Every birthday in our family brought a new star book, until now we +have about a dozen--all of them interesting and not one of them having +mathematics that children cannot understand. So I think we have spent on +stars fifteen dollars more than we needed to spend (but I'm glad we did +it), and I think we have had about two hundred dollars worth of fun! +Yes, when I think what young people spend on ball games, fishing, +tennis, skating, and all the other things that children love, I am sure +our family has had about two hundred dollars worth of fun out of stars. +And there is more to come! + +You would laugh to know why I enjoy stars so much. I have always studied +birds and flowers and trees and rocks and shells so much that I was +afraid to get interested in stars. I thought it wouldn't rest me. But +it's a totally different kind of science from any I ever studied! There +are no families, genera, and species among the stars, thank Heaven! +That's one reason they refresh me. Another is that no one can press them +and put them in a herbarium, or shoot them and put them in a museum. And +another thing about them that brings balm to my spirit is that no human +being can destroy their beauty. No one can "sub-divide" Capella and fill +it with tenements. No one can use Vega for a bill-board. Ah, well! we +must not be disturbed if every member of our family has a different +point of view toward the stars; we can all enjoy and love them in our +own ways. + +How would you like to start a Star Club like ours? You ought to be able +to persuade your family to form one, because it need not cost a cent. +Perhaps this book will interest them all, but the better way is for you +to read about one constellation and then go out with some of the family +and find it. This book does not tell about wonderful things you can +never see; it tells about the wonderful things all of us can see. + +I wish you success with your Star Club. Perhaps your uncles and aunts +will start clubs, too. We have three Star Clubs in our family--one in +New York, one in Michigan, and one in Colorado. Last winter the +"Colorado Star Gazers" sent this challenge to the "New Jersey +Night-Owls:" "_We bet you can't see Venus by daylight!_" + +That seemed possible, because during that week the "evening star" was by +far the brightest object in the sky. But father and daughter searched +the sky before sunset in vain, and finally we had to ask the "Moonstruck +Michiganders" how to see Venus while the sun was shining. Back came +these directions on a postal-card: "Wait until it is dark and any one +can see Venus. Then find some tree, or other object, which is in line +with Venus and over which you can just see her. Put a stake where you +stand. Next day go there half an hour before sunset, and stand a little +to the west. You will see Venus as big as life. The next afternoon you +can find her by four o'clock. And if you keep on you will see her day +before yesterday!" + +That was a great "stunt." We did it; and there are dozens like it you +can do. And that reminds me that father was mistaken about our interest +lasting only two years. We know that it will not die till we do. For, +even if we never get a telescope, there will always be new things to +see. Our club has still to catch Algol, the "demon's eye," which goes +out and gleams forth every three days, because it is obscured by some +dark planet we can never see. And we have never yet seen Mira the +wonderful, which for some mysterious reason dies down to ninth magnitude +and then blazes up to second magnitude every eleventh month. + +Ah, yes, the wonders and the beauties of astronomy ever deepen and +widen. Better make friends with the stars now. For when you are old +there are no friends like old friends. + + + + +THE DIPPERS AND THE POLE STAR + + +I never heard of any boy or girl who didn't know the Big Dipper. But +there is one very pleasant thing about the Dipper which children never +seem to know. With the aid of these seven magnificent stars you can find +all the other interesting stars and constellations. So true is this that +a book has been written called "The Stars through a Dipper." + +To illustrate, do you know the _Pointers_? I mean the two stars on the +front side of the Dipper. They point almost directly toward the Pole +star, or North star, the correct name of which is Polaris. Most children +can see the Pole star at once because it is the only bright star in that +part of the heavens. + +But if you can't be sure you see the right one, a funny thing happens. +Your friend will try to show you by pointing, but even if you look +straight along his arm you can't always be sure. And then, if he tries +to tell you how far one star is from another, he will try to show you by +holding his arms apart. But that fails also. And so, we all soon learn +the easiest and surest way to point out stars and measure distances. + +The easiest way to tell any one how to find a star is to get three +stars in a straight line, or else at right angles. + +The surest way to tell any one how far one star is from another is by +"degrees." You know what degrees are, because every circle is divided +into 360 of them. And if you will think a moment, you will understand +why we can see only half the sky at any one time, or 180 degrees, +because the other half of the sky is on the other side of the earth. +Therefore, if you draw a straight line from one horizon, clear up to the +top of the sky and down to the opposite horizon, it is 180 degrees long. +And, of course, it is only half that distance, or 90 degrees, from +horizon to zenith. (Horizon is the point where earth and sky seem to +meet, and zenith is the point straight over your head.) + +Now ninety degrees is a mighty big distance in the sky. The Pole star is +nothing like ninety degrees from the Dipper. It is only twenty-five +degrees, or about five times the distance between the Pointers. And now +comes the only thing I will ask you to remember. Look well at the two +Pointers, because the distance between them, five degrees, is the most +convenient "foot rule" for the sky that you will ever find. Most of the +stars you will want to talk about are from two to five times that +distance from some other star that you and your friends are sure of. +Perhaps this is a little hard to understand. If so, read it over several +times, or get some one to explain it to you, for when you grasp it, it +will unlock almost as many pleasures as a key to the store you like the +best. + +Now, let's try our new-found ruler. Let us see if it will help us find +the eighth star in the Dipper. That's a famous test of sharp eyes. I +don't want to spoil your pleasure by telling you too soon where it is. +Perhaps you would rather see how sharp your eyes are before reading any +further. But if you can't find the eighth star, I will tell you where to +look. + +Look at the second star in the Dipper, counting from the end of the +handle. That is a famous star called Mizar. Now look all around Mizar, +and then, if you can't see a little one near it, try to measure off one +degree. To do this, look at the Pointers and try to measure off about a +fifth of the distance between them. Then look about one degree (or less) +from Mizar, and I am sure you will see the little beauty--its name is +Alcor, which means "the cavalier" or companion. The two are sometimes +called "_the horse and rider_"; another name for Alcor is Saidak, which +means "the test." I shall be very much disappointed if you cannot see +Saidak, because it is not considered a hard test nowadays for sharp +eyes. + +Aren't these interesting names? Mizar, Alcor, Saidak. They sound so +Arabian, and remind one of the "Arabian Nights." At first, some of them +will seem hard, but you will come to love these old names. I dare say +many of these star names are 4,000 years old. Shepherds and sailors +were the first astronomers. The sailors had to steer by the stars, and +the shepherds could lie on the ground and enjoy them without having to +twist their necks. They saw and named Alcor, thousands of years before +telescopes were invented, and long before there were any books to help +them. They saw the demon star, too, which I have never seen. It needs +patience to see those things; sharp eyes are nothing to be proud of, +because they are given to us. But patience is something to be eager +about, because it costs us a lot of trouble to get it. + +Let's try for it. We've had a test of sight. Now let's have a test of +patience. It takes more patience than sharpness of sight to trace the +outline of the Little Dipper. It has seven stars, too, and the Pole star +is in the end of the handle. Do you see two rather bright stars about +twenty-five degrees from the Pole? I hope so, for they are the only +brightish stars anywhere near Polaris. Well, those two stars are in the +outer rim of the Little Dipper. Now, I think you can trace it all; but +to make sure you see the real thing, I will tell you the last secret. +The handle of the Big Dipper is bent _back_; the handle of the Little +Dipper is bent _in_. + +Now, if you have done all this faithfully, you have worked hard enough, +and I will reward you with a story. Once upon a time there was a +princess named Callisto, and the great god Jupiter fell in love with +her. Naturally, Jupiter's wife, Juno, wasn't pleased, so she changed the +princess into a bear. But before this happened, Callisto became the +mother of a little boy named Arcas, who grew up to be a mighty hunter. +One day he saw a bear and he was going to kill it, not knowing that the +bear was really his own mother. Luckily Jupiter interfered and saved +their lives. He changed Arcas into a bear and put both bears into the +sky. Callisto is the Big Bear, and Arcas is the Little Bear. But Juno +was angry at that, and so she went to the wife of the Ocean and said, +"Please, never let these bears come to your home." So the wife of the +Ocean said, "I will never let them sink beneath the waves." And that is +why the Big and the Little Dipper never set. They always whirl around +the Pole star. And that is why you can always see them, though some +nights you would have to sit up very late. + +Is that a true story? No. But, I can tell you a true one that is even +more wonderful. Once upon a time, before the bear story was invented and +before people had tin dippers, they used to think of the Little Dipper +as a little dog. And so they gave a funny name to the Pole star. They +called it Cynosura, which means "the dog's tail." We sometimes say of a +great man, "he was the cynosure of all eyes," meaning that everybody +looked at him. But the original cynosure was and is the Pole star, +because all the stars in the sky seem to revolve around it. The two +Dippers chase round it once every twenty-four hours, as you can convince +yourself some night when you stay up late. So that's all for to-night. + +What! You want another true story? Well, just one more. Once upon a time +the Big Dipper was a perfect cross. That was about 50,000 years ago. +Fifty thousand years from now the Big Dipper will look like a steamer +chair. How do I know that? Because, the two stars at opposite ends of +the Dipper are going in a direction different from the other five stars. +How do I know that? Why, I don't know it. I just believe it. There are +lots of things I don't know, and I'm not afraid to say so. I hope you +will learn how to say "I don't know." It's infinitely better than +guessing; it saves trouble, and people like you better, because they see +you are honest. I don't know how the stars in the Big Dipper are moving, +but the men who look through telescopes and study mathematics say the +end stars do move in a direction opposite to the others, and they say +the Dipper _must_ have looked like a cross, and will look like a dipper +long, long after we are dead. And I believe them. + + + + +CONSTELLATIONS YOU CAN ALWAYS SEE + + +There are forty-eight well known constellations, but of these only about +a dozen are easy to know. I think a dozen is quite enough for children +to learn. And therefore, I shall tell you how to find only the showiest +and most interesting. + +The best way to begin is to describe the ones that you can see almost +every night in the year, because you may want to begin any month in the +year, and you might be discouraged if I talked about things nobody could +see in that month. There are five constellations you can nearly always +see, and these are all near the Pole star. + +Doubtless you think you know two of them already--the Big and the Little +Dipper. Ah, I forgot to tell you that these dippers are not the real +thing. They are merely parts of bigger constellations and their real +names are Great Bear and Little Bear. The oldest names are the right +ones. Thousands of years ago, when the Greeks named these groups of +stars, they thought they looked like two bears. I can't see the +resemblance. + +But for that matter all the figures in the sky are disappointing. The +people who named the constellations called them lions, and fishes, and +horses, and hunters, and they thought they could see a dolphin, a +snake, a dragon, a crow, a crab, a bull, a ram, a swan, and other +things. But nowadays we cannot see those creatures. We can see the stars +plainly enough, and they do make groups, but they do not look like +animals. I was greatly disappointed when I was told this; but I soon got +over it, because new wonders are always coming on. I think the only +honest thing to do is to tell you right at the start that you cannot see +these creatures very well. You will spoil your pleasure unless you take +these resemblances good-naturedly and with a light heart. And you will +also spoil your pleasure if you scold the ancients for naming the +constellations badly. Nobody in the world would change those old names +now. There is too much pleasure in them. Besides, I doubt if we could do +much better. I believe those old folks were better observers than we. +And I believe they had a lighter fancy. + +Let us, too, be fanciful for once. I have asked my friend, Mrs. Thomas, +to draw her notion of some of these famous creatures of the sky. You can +draw your idea of them too, and it is pleasant to compare drawings with +friends. There is only one way to see anything like a Great Bear. You +have to imagine the Dipper upside down and make the handle of the Dipper +serve for the Bear's tail. What a funny bear to drag a long tail on the +ground! Miss Martin says he looks more like a chubby hobby-horse. You +will have to make the bowl of the Dipper into hind legs and use all the +other stars, somehow, to make a big, clumsy, four-legged animal. And +what a monster he is! He measures twenty-five degrees from the tip of +his nose to the root of his tail. Yes, all those miscellaneous faint +stars you see near the Big Dipper belong to the Great Bear. + +[Illustration: Orion fighting the Bull. Above are Orion's two dogs] + +[Illustration: The Little Bear, the Queen in her chair, the Twins and +the Archer] + +How the Great Bear looked to the people who named it thousands of years +ago, we probably shall never know. They left no books or drawings, so +far as I know. But in every dictionary and book on astronomy you can +find these bears and other animals drawn so carefully and beautifully +that it seems as if they _must_ be in the sky, and we must be too dull +to see them. It is not so. Look at the pictures in this book and, you +will see that the stars do not outline the animals. Many of them come at +the wrong places. And so it is with all the costly books and charts and +planispheres. It is all very interesting, but it isn't true. It's just +fancy. And when you once understand that it isn't true, you will begin +to enjoy the fancy. Many a smile you will have, and sometimes a good +laugh. For instance, the English children call the Dipper "Charles's +wain" or "the wagon." And the Romans called it "the plough." They +thought of those seven stars as oxen drawing a plough. + +Well, that's enough about the two Bears. I want to tell you about the +other three constellations you can nearly always see. These are the +Chair, the Charioteer, and Perseus (pronounced _per'soos_). + +The Chair is the easiest to find, because it is like a very bad W, and +it is always directly opposite the big Dipper, with the Pole star half +way between the two constellations. There are five stars in the W, and +to make the W into a Chair you must add a fainter star which helps to +make the square bottom of the chair. But what a crazy piece of +furniture! I have seen several ways of drawing it, but none of them +makes a comfortable chair. I should either fall over backward, or else +the back of the chair would prod me in the small of my back. The correct +name of this constellation is Cassiopeia's Chair. + +I think this is enough to see and enjoy in one night. To-morrow night +let us look for the Charioteer. + +I love the Charioteer for several reasons. One is that it makes a +beautiful pentagon, or five-sided figure, with its five brightest stars. +Another is that it contains the second-brightest star in the northern +part of the heavens, Capella. The only star in the north that is +brighter is Vega, but Vega is bluish white or creamy. + +If you haven't already found the five-sided figure, I will tell you how +to find Capella. Suppose you had a gun that would shoot anything as far +as you wish. Shoot a white string right through the Pointers and hit the +Pole star. Then place your gun at the Pole star and turn it till it is +at right angles to that string you shot. Aim away from the big Dipper, +shoot a bullet forty-five degrees and it will hit Capella. + +If that plan doesn't work, try this. Start with the star that is at the +bottom of the Dipper and nearest the handle. Draw a line half-way +between the two Pointers and keep on till you come to the first bright +star. This is Capella, and the distance is about fifty degrees. + +Capella means "a kid," or "little goat," and that reminds me of the +third reason why I enjoy so much the constellation of which Capella is +the brightest star. In the old times they sometimes called this +five-sided figure "the goat-carrier." And the shepherds thought they +could see a man carrying a little goat in his left hand. I am sure you +can see the kid they meant. It is a triangle of faint stars which you +see near Capella. That's enough for to-night. + +To-morrow night let us look for Perseus. I dare say you know that old +tale about Perseus rescuing the princess who was chained upon a rock. +(He cut off the snaky head of Medusa and showed it to the dragon that +was going to devour the princess, and it turned the monster to stone. +Remember?) Well, there are constellations named after all the people in +that story, but although they contain many showy stars, I could never +make them look like a hero, a princess, a king, and a queen. I do not +even try to trace out all of Perseus. For I am satisfied to enjoy a very +beautiful part of it which is called the "Arc of Perseus." + +An arc, you know, is a portion of a circle. And the way to find this arc +is to draw a curve from Capella to Cassiopeia. On nights that are not +very clear I can see about seven stars in this Arc of Perseus. And the +reason I love it so much is that it is the most beautiful thing, when +seen through an opera-glass, that I know. You could never imagine that a +mere opera-glass would make such a difference. The moment I put it to my +eyes about a dozen more stars suddenly leap into my sight in and near +the Arc of Perseus. That's enough. No more stories to-night. + + + + +WINTER CONSTELLATIONS + + +By winter constellations I mean those you can see in winter at the +pleasantest time--the early evening. And I want you to begin with the +Northern Cross. I hope you can see this before Christmas, for, after +that, it may be hidden by trees or buildings in the west and you may not +see it again for a long while. This is because the stars seem to rise in +the east and set in the west. To prove this, choose some brilliant star +you can see at five or six o'clock; get it in line with some bush or +other object over which you can just see it. Put a stake where you +stand, and then go to the same spot about eight o'clock or just before +you go to bed. You can tell at once how much the star seems to have +moved westward. + +Another thing, every star rises four minutes later every night, and +therefore the sky looks a little different at the same hour every +evening. The stars in the north set for a short time only, but when +those toward the south set they are gone a long time. For instance, the +brightest star of all is Sirius, the Dog Star, which really belongs to +the southern hemisphere. There are only about three months in the year +when children who go to bed by seven o'clock can see it--January, +February, and March. + +So now you understand why I am so eager that you should not miss the +pleasure of seeing the famous Northern Cross. But although it is a big +cross, and easy to find, after you know it, I have never yet known a boy +who could show it to another boy simply by pointing at it. The surest +and best way to find it is learn three bright stars first--Altair, Vega, +and Deneb. + +Altair is the brightest star in the Milky Way. It is just at the edge of +the Milky Way, and you are to look for three stars in a straight line, +with the middle one brightest. Those three stars make the constellation +called "the Eagle." The body of the eagle is Altair, and the other two +stars are the wings. I should say that Altair is about five degrees from +each of his companions. It is worth half an hour's patient search to +find the Eagle. Now these three stars in the Eagle point straight toward +the brightest star in the northern part of the sky--Vega. + +To make sure of it, notice four fainter stars near it which make a +parallelogram--a sort of diamond. These stars are all part of a +constellation called "the Lyre." If you try to trace out the old musical +instrument, you will be disappointed; but here is a game worth while. +Can you see a small triangle made by three stars, of which Vega is one? +Well, one of those stars is double, and with an opera-glass you can see +which it is. On very clear nights some people with very sharp eyes can +see them lying close together, but I never could. + +At last we are ready to find the celebrated Northern Cross. First draw a +line from Altair to Vega. Then draw a line at right angles to this, +until you come to another bright star--Deneb--which is about as far from +Vega as Vega is from Altair. Now this beautiful star, Deneb, is the top +of the Northern Cross. I can't tell you whether the Cross will be right +or wrong side up when you see it, or on its side. For every +constellation is likely to change its position during the night, as you +know from watching the Dipper. But you can tell the Cross by these +things. There are six stars in it. It is like a kite made of two sticks. +There are three stars in the crosspiece and four in the long piece. +Deneb, the brightest star in the cross, is at the top of the long stick. + +But you mustn't expect to see a perfect cross. There is one star that is +a little out of place, and sometimes my fingers fairly "itch to put it +where it belongs." It is the one that ought to be where the long stick +of your kite is tacked to the crosspiece. And one of the stars is +provokingly faint, but you can see it. Counting straight down the long +piece, it is the third one from Deneb that is faint. It is where it +ought to be, but I should like to make it brighter. Have you the Cross +now? If not, have patience. You can't be a "true sport" unless you are +patient. You can't be a great ball-player, or hunter, or any thing else, +without resisting, every day, that sudden impulse to "quit the game" +when you lose. Be a "good loser," smile and try again. That is better +than to give up, or to win by cheating or sharp practice. + +This is the last thing I want you to see in the northern part of the +sky; and if you have done a good job, let us celebrate by having a +story. + +Once upon a time a cross didn't mean so much to the world as it does +now. That was before Christ was born. In those old times people did not +think of the Northern Cross as a cross. They thought of it as a Swan, +and you can see the Swan if you turn the Cross upside down. Deneb will +then be in the tail of the Swan, and the two stars which used to be at +the tips of the crosspiece now become the wings. Is that a true story? +Yes. If we lived in Arabia the children there could tell us what Deneb +means. It means "the tail." + +Another story? Well, do you see the star in the beak of the Swan, or +foot of the Cross? What color is it? White? Well, they say this white +star is really made up of two stars--one yellow and the other blue. That +is one reason I want to buy a telescope when I can afford it, for even +the smallest telescope will show that. And Mr. Serviss says that even a +strong field-glass will help any one see this wonder. + +I can't tell you about all the winter constellations in one chapter. We +have made friends of the northern ones. Now let's see the famous +southern ones. And let's start a new chapter. + + + + +ORION, HIS DOGS, AND THE BULL + + +The most gorgeous constellation in the whole sky is Orion. I really pity +any one who does not know it, because it has more bright stars in it +than any other group. Besides, it doesn't take much imagination to see +this mighty hunter fighting the great Bull. I dare say half the people +in the United States know Orion and can tell him as quick as they see +him by the famous "belt of Orion." + +This belt is made of three stars, each of which is just one degree from +the next. That is why the English people call these three stars "the ell +and yard." Another name for them is "the three kings." You can see the +"sword of Orion" hanging down from his belt. + +As soon as you see these things you will see the four bright stars that +outline the figure of the great hunter, but only two of them are of the +first magnitude. The red one has a hard name--Betelgeuse (pronounced +_bet-el-guz'_). That is a Frenchified word from the Arabic, meaning +"armpit," because this star marks the right shoulder of Orion. The other +first-magnitude star is the big white one in the left foot. Its name is +Rigel (pronounced _re'-jel_) from an Arabian word meaning "the foot." + +You can see the giant now, I am sure. Over his left arm hangs a lion's +skin which he holds out to shield him from the bull's horns. See the +shield--about four rather faint stars in a pretty good curve? Now look +for his club which he holds up with his right hand so as to smite the +bull. See the arm and the club--about seven stars in a rather poor +curve--beyond the red star Betelgeuse? Now you have him, and isn't he a +wonder! + +It is even easier to see the Bull which is trying to gore Orion. Look +where Orion is threatening to strike, and you will see a V. How many +stars in that V? Five. And which is the brightest? That red one at the +top of the left branch of the V? Yes. That V is the face of the Bull and +that red star is the baleful eye of the angry Bull which is lowering his +head and trying to toss Orion. The name of that red eye is Aldebaran +(pronounced _al-deb'-ar-an_). + +I wish Aldebaran meant "red eye," but it doesn't. It is an old Arabian +word meaning the "hindmost," or the "follower," because every evening it +comes into view about an hour after you can see the famous group of +stars called the Pleiades, which are in the shoulder of the Bull. + +I do not care to trace the outline of this enormous bull, but his horns +are a great deal longer than you think at first. If you will extend the +two arms of that V a long way you will see two stars which may be called +the tips of his horns. One of these stars really belongs in another +constellation--our old friend the Charioteer, the one including +Capella. Wow! what a pair of horns! + +But now we come to the daintiest of all constellations--the Seven +Sisters, or Pleiades (pronounced _plee'-a-deez_). + +I can see only six of them, and there is a famous old tale about the +"lost Pleiad." But I needn't describe them. Every child finds them by +instinct. Some compare them to a swarm of bees; some to a rosette of +diamonds; some to dewdrops. But I would not compare them to a dipper as +some do, because the real Little Dipper is very different. The light +that seems to drip from the Pleiades is quivering, misty, romantic, +magical. No wonder many children love the Pleiades best of all the +constellations. No wonder the poets have praised them for thousands of +years. The oldest piece of poetry about them that I know of was written +about 1,500 years before Christ. You can find it in the book of Job. But +the most poetic description of the Pleiades that I have ever read is in +Tennyson's poem "Locksley Hall," in which he says they "glitter like a +swarm of fireflies tangled in a silver braid." + +There are a great many old tales about the lost Pleiad. One is that she +veiled her face because the ancient city of Troy was burned. Another +story says she ceased to be a goddess when she married a man and became +mortal. Some people think she was struck by lightning. Others believe +the big star, Canopus, came by and ran away with her. Still others +declare she was a new star that appeared suddenly once upon a time, and +after a while faded away. + +For myself, I do not believe any of these stories. One reason why I +don't is that a seventh star is really there, and many people can really +see it. Indeed, there are some people so sharp-eyed that on clear nights +they can see anywhere from eight to eleven. And, what is more, they can +draw a map or chart showing just where each star seems to them to be. + +But the most wonderful stories about the Pleiades are the true stories. +One is that there are really more than 3,000 stars among the Pleiades. +Some of them can be seen only with the biggest telescopes. Others are +revealed only by the spectroscope. And some can be found only by means +of photography. + +But the most amazing thing about the Pleiades is the distances between +them. They look so close together that you would probably say "the moon +seems bigger than all of them put together." Sometimes the moon comes +near the Pleiades, and you expect that the moon will blot them all out. +But the astronomers say the full moon sails through the Pleiades and +covers only one of them at a time, as a rule. They even say it is +possible for the moon to pass through the Pleiades without touching one +of them! I should like to see that. If anything like it is going to +occur, the magazine I spoke of in the first chapter will tell me about +it. And you'd better believe I will stay up to see that, if it takes all +night! + +There are two more constellations in the southern part of the sky that +ought to be interesting, because they are the two hunting dogs that help +Orion fight the Bull. But I can't trace these animals, and I don't +believe it is worth while. The brightest stars in them everybody can see +and admire--Sirius, the Bigger Dog, and Procyon, the Smaller Dog. + +Every one ought to know Sirius, because he is the brightest star of all. +(Of course, he is not so bright as Venus and Jupiter, but they are +planets.) To find him, draw a line from the eye of the Bull through the +belt of Orion and extend it toward the southeast about twenty degrees. +They call him the Dog star because he follows the heels of Orion. And +people still call the hottest days of summer "dog days" because 400 +years before Christ the Romans noticed that the Dog star rose just +before the sun at that time. The Romans thought he chased the sun across +the sky all day and therefore was responsible for the great heat. But +that was a foolish explanation. And so is the old notion that dogs are +likely to go mad during the dog days "because the dog star is in the +ascendant." So is the idea that Sirius is an unlucky star. + +There are no lucky or unlucky stars. These are all superstitions, and we +ought to be ashamed to believe any superstition. Yet for thousands of +years before we had public schools and learned to know better, people +believed that every one was born under a lucky star or an unlucky one, +and they believe that farmers ought to plant or not plant, according to +the size of the moon. Now we know that is all bosh. Those old +superstitions have done more harm than good. One of the most harmful was +the belief in witches. Let us resolve never to be afraid of these old +tales, but laugh at them. + +Why should anybody be afraid of anything so lovely as Sirius? I used to +think Sirius twinkled more than any other star. But that was bad +reasoning on my part. I might have noticed that every star twinkles more +near the horizon than toward the zenith. I might have noticed that stars +twinkle more on clear, frosty nights than when there is a little uniform +haze. And putting those two facts together I might have reasoned that +the stars never really twinkle at all; they only seem to. I might have +concluded that the twinkling is all due to the atmosphere--that blanket +of air which wraps the earth around. The nearer the earth, the thicker +the air, and the more it interferes with the light that comes to us from +the stars. + +They say that Sirius never looks exactly alike on two successive nights. +"It has a hundred moods," says Mr. Serviss, "according to the state of +the atmosphere. By turns it flames, it sparkles, it glows, it blazes, it +flares, it flashes, it contracts to a point, and sometimes when the air +is still, it burns with a steady white light." (Quotation somewhat +altered and condensed.) + +It is a pity that so fine a star as Procyon should be called the +"Smaller Dog," because it suffers unjustly by comparison with Sirius. If +it were in some other part of the sky we might appreciate it more, +because it is brighter than most of the fifteen first-magnitude stars we +can see. My brother William has grown to love it, but perhaps that is +because he always "sympathizes with the under dog." He was the youngest +brother and knows. And curiously enough he was nicknamed "the dog"--just +why, I don't know. + +To find Procyon, drawn a line from Sirius northeast about twenty +degrees. And to make sure, draw one east from Betelgeuse about the same +distance. These three stars make a triangle of which the sides are +almost equal. + +The name Procyon means "before the dog" referring to the fact that you +can see him fifteen or twenty minutes earlier every night than you can +see Sirius. + +The only kind word about Procyon I have heard in recent years was in +connection with that miserable business of Dr. Cook and the North Pole. +A Captain Somebody-or-other was making observations for Dr. Cook, and he +wanted to know what time it was. He had no watch and didn't want to +disturb any one. So he looked out of the window and saw by the star +Procyon that it was eleven o'clock. + +That sounds mysterious, but it is easy if you have a planisphere like +ours. Last winter when we were all enjoying Orion, the Bull, and the two +Dogs, I used to whirl the planisphere around to see where they would be +at six o'clock at night, at eight, at ten, at midnight, and even at six +o'clock in the morning. And so, if I waked up in the night I could tell +what time it was without even turning my head. Sometimes I looked out of +my window, saw Orion nearly overhead and knew it must be midnight. And +sometimes I woke up just before daybreak and saw the great Bull backing +down out of sight in the west, the mighty Hunter still brandishing his +club, and his faithful Dogs following at his heels. + + + + +SEVEN FAMOUS CONSTELLATIONS + + +There are only seven more constellations that seem to me interesting +enough for every one to know and love all his life. These are: + + The Lion (Spring) + + The Twins (Spring) + + The Virgin (Summer) + + The Herdsman (Summer) + + The Northern Crown (Summer) + + The Scorpion (Summer) + + Southern Fish (Autumn) + +I have named the seasons when, according to some people, these +constellations are most enjoyable. But these are not the only times when +you can see them. (If you had that seventy-five-cent planisphere, now, +you could always tell which constellations are visible and just where to +find them.) No matter what time of year you read this chapter, it is +worth while to go out and look for these marvels. You can't possibly +miss them all. + +Have you ever seen a Sickle in the sky? It's a beauty, and whenever I +have seen it it has been turned very conveniently for me, because I am +left-handed. It is so easy to find that I am almost ashamed to tell. But +if you need help, draw a line through the Pointers backward, away from +the Pole star, about forty degrees, and it will come a little west of +the Sickle. The Sickle is only part of the Lion--the head and the +forequarters. Only fanciful map-makers can trace the rest of the Lion. +The bright star at the end of the handle is Regulus, which means "king," +from the stupid old notion that this star ruled the lives of men. To +this day people speak of the "Royal Star," meaning Regulus. And at the +end of this chapter I will tell you about three other stars which the +Persians called "royal stars." + +Another constellation which children particularly love is the +Twins--Castor and Pollux. But the sailors got there first! For thousands +of years the twins have been supposed to bring good luck to sailors. I +don't believe a word of it. But I do know that sailors gloat over Castor +and Pollux, and like them better than any other stars. The whole +constellation includes all the stars east of the Bull and between the +Charioteer and Procyon. But another way to outline the twins is to look +northeast of Orion where you will see two rows of stars that run nearly +parallel. To me the brothers seem to be standing, but all the old +picture-makers show them sitting with their arms around each other, the +two brightest stars being their eyes. The eyes are about five degrees +apart--the same as the Pointers. + +Pollux is now brighter than Castor, but for thousands of years it was +just the other way. It is only within three hundred years that this +change has taken place. Whether Castor has faded or Pollux brightened, +or both, I do not know. Anyhow, Castor is not quite bright enough to be +a first magnitude star. Three hundred years is a short time in the +history of man, and only a speck in the history of the stars. Three +hundred years ago they killed people in Europe just because of the +church they went to. That was why the Pilgrim Fathers sailed from +England in 1620, and made the first permanent settlement in America, +except, of course, Jamestown, Va., in 1607. + +There are plenty of stories about old Castor and Pollux, and, like all +the other myths, they conflict, more or less. But all agree that these +two brothers went with Jason in the ship Argo, shared his adventures and +helped him get the golden fleece. And all agree that Castor and Pollux +were "born fighters." And that is why the Roman soldiers looked up to +these stars and prayed to them to help them win their battles. + +Now for the four summer constellations every one ought to know. The +first thing to look for is two famous red or reddish stars--Arcturus and +Antares. + +The way you find Arcturus is amusing. Look for the Big Dipper and find +the star at the bottom of the dipper nearest the handle. Got it? Now +draw a curve that will connect it with all the stars in the handle, and +when you come to the end of the handle keep on till you come to the +first very bright star--about twenty-five degrees. That is the monstrous +star Arcturus, probably the biggest and swiftest star we can ever see +with the naked eye in the northern hemisphere. He is several times as +big as our sun, and his diameter is supposed to be several million +miles. He is called a "runaway sun," because he is rushing through space +at the rate of between two hundred and three hundred miles a second. +That means between seventeen and thirty-four million miles a day! + +He is coming toward us, too! At such a rate you might think that +Arcturus would have smashed the earth to pieces long ago. But he is +still very far away, and there is no danger. Some people say that if Job +were to come to life, the sky would seem just the same to him as it did +3,400 years ago. The only difference he might notice would be in +Arcturus. That would seem to him out of place by a distance about three +times the apparent diameter of the moon. + +Some people believe this because Job said, "Canst thou guide Arcturus +with his sons?" and therefore they imagine that he meant this red star. +But I believe he meant the Big Dipper. For in King James's time, when +the Bible was translated into English, the word "Arcturus" meant the Big +Dipper or rather the Great Bear. And for centuries before it meant the +Great Bear. One proof of it is that "Arcturus" comes from an old Greek +word meaning "bear"--the same word from which we get arctic. It is only +within a few hundred years that astronomers have agreed to call the +Great Bear "Ursa Major," and this red star Arcturus. So I think all the +books which say Job mentioned this red star are mistaken. I believe +Webster's Dictionary is correct in this matter, and I believe the +Revised Version translates Job's Hebrew phrase more correctly when it +says, "Canst thou guide the Bear with her train?" + +Anyhow, Arcturus is a splendid star--the brightest in the constellation +called the "Herdsman" or Booetes. It is not worth while to trace the +Herdsman, but here is an interesting question. Is Arcturus really red? +The books mostly say he is yellow. They say he looks red when he is low +in the sky, and yellow when he is high. How does he look to you? More +yellow than red? + +Well, there's no doubt about Antares being red. To find him, draw a long +line from Regulus through Arcturus to Antares, Arcturus being more than +half way between the other two. But if Regulus and the Sickle are not +visible, draw a line from Altair, at right angles to the Eagle, until +you come to a bright star about sixty degrees away. You can't miss +Antares, for he is the only red star in that part of the sky. + +Antares belongs to a showy constellation called the Scorpion. I cannot +trace all the outline of a spider-like creature, but his poisonous tail +or "stinger" is made by a curved line of stars south and east of +Antares. And you can make a pretty fan by joining Antares to several +stars in a curve which are west of Antares and a little north. There is +an old tale that this Scorpion is the one that stung Orion to death when +he began to "show off" and boast that there was no animal in the world +that could kill him. + +Another very bright star in the southern part of the sky is Spica. To +find it, start with the handle of the Dipper, and making the same +backward curve which helped you to find Arcturus, keep on till you come +to the white star Spica--say thirty degrees beyond Arcturus. This is the +brightest star in the constellation called "the Virgin." It is not worth +while trying to trace her among nearly forty faint stars in this +neighbourhood. But she is supposed to be a winged goddess who holds up +in her right hand an _ear of wheat_, and that is what Spica means. + +Now for an autumn constellation--the Southern Fish. I don't care if you +fail to outline a fish, but I do want you to see the bright star that is +supposed to be in the fish's mouth. And I don't want you to balk at its +hard name--Fomalhaut (pronounced _fo'-mal-o_). It is worth a lot of +trouble to know it as a friend. To find it, you have to draw an +exceedingly long line two-thirds of the way across the whole sky. Start +with the Pointers. Draw a line through them and the Pole star and keep +clear on until you come to a solitary bright star rather low down in the +south. That is Fomalhaut. It looks lonely and is lonely, even when you +look at it through a telescope. + +And now for the last story. Once upon a time the Persians thought there +must be four stars that rule the lives of men. So they picked out one in +the north and one in the south and one in the east and one in the west, +just as if they were looking for four bright stars to mark the points of +the compass. If you want to find them yourself without my help don't +read the next sentence, but shut this book and go out and see. Then +write down on a piece of paper the stars you have selected and compare +them with the list I am about to give. Here are the four royal stars of +the Persians: Fomalhaut for the north, Regulus for the south, Aldebaran +for the east, and Antares for the west. + +Why doesn't this list agree with yours? Because Persia is so far south +of where we live. Ah, there are very few things that are absolutely +true. Let's remember that and not be too sure: for everything depends +upon the point of view! I hope you will see Fomalhaut before Christmas, +before he disappears in the west. He is with us only five months and is +always low--near the horizon. But the other seven months in the year he +gladdens the children of South America and the rest of the southern +hemisphere, for they see him sweeping high and lonely far up into their +sky and down again. + +But the loveliest of all the constellations described in this chapter is +the Northern Crown. It is not a perfect crown--only about half a +circle--but enough to suggest a complete ring. Look for it east of +Arcturus. I can see seven or eight stars in the half-circle, one of +which is brighter than all the others. That one is called "the Pearl." +The whole constellation is only fifteen degrees long, but "fine things +come in small packages"; and children grow to love the Northern Crown +almost as much as they love the Pleiades. + + + + +THE TWENTY BRIGHTEST STARS + + +If you have seen everything I have described so far, you have reason to +be happy. For now you know sixteen of the most famous constellations and +fifteen of the twenty brightest stars. There are only twenty stars of +the first magnitude. "Magnitude" ought to mean size, but it doesn't. It +means brightness--or rather the apparent brightness--of the stars when +seen by us. The word magnitude was used in the old days before +telescopes, when people thought the brighter a star is the bigger it +must be. Now we know that the nearer a star is to us the brighter it is, +and the farther away the fainter. Some of the bright stars are +comparatively near us, some are very far. Deneb and Canopus are so far +away that it takes over three hundred years for their light to reach us. +What whoppers they must be--many times as big as our sun. + +Here is a full list of the twenty stars of the first magnitude arranged +in the order of their brightness. You will find this table very useful. + + ----------------+---------------+-------------+-------------------------- + Stars | Pronounced |Constellation| Interesting facts + ----------------+---------------+-------------+-------------------------- + Sirius | _sir'i-us_ | Big Dog | Brightest star. Nearest + | | | star visible in Northern + | | | hemisphere + Canopus* | _ca-no'pus_ | Ship Argo | Perhaps the largest body + | | | in universe + Alpha Centauri* | _al'fa | | + | sen-taw're_ | Centaur | Nearest star. Light four + | | | years away + Vega | _ve'ga_ | Lyre | Brightest star in the + | | | Northern sky. Bluish + Capella | _ca-pell'a_ | Charioteer | Rivals Vega, but opposite + | | | the pole. Yellowish + Arcturus | _ark-tu'rus_ | Herdsman | Swiftest of the bright + | | | stars. 200 miles a second + Rigel | _re'jel_ | Orion | Brightest star in Orion. + | | | White star in left foot + Procyon | _pro'si-on_ | Little Dog | Before the dog. Rises a + | | | little before Sirius + Achernar* | _a-ker'nar_ | River Po | Means the end of the river + Beta Centauri* | _ba'ta | | + | sen-taw're_ | Centaur | This and its mate point to + | | | the Southern Cross + Altair | _al-tare'_ | Eagle | Helps you find Vega and + | | | Northern Cross + Betelgeuse | _bet-el-guz'_ | Orion | Means "armpit." The red + | | | star in the right shoulder + Alpha Crucis* | _al'fa | Southern | + | cru'sis_ | Cross | At the base of the most + | | | famous Southern + | | | constellation + Aldebaran | _al-deb'a-ran_| Bull | The red eye in the V + Pollux | _pol'lux_ | Twins | Brighter than Castor + Spica | _spi'ca_ | Virgin | Means ear of wheat + Antares | _an-ta'rez_ | Scorpion | Red star. Name means + | | | "looks like Mars" + Fomalhaut | _fo'mal-o_ | Southern | + | | Fish | The lonely star in the + | | | Southern sky + Deneb | _den'eb_ | Swan | Top of Northern Cross, + | | | or tail of Swan + Regulus | _reg'u-lus_ | Lion | The end of the handle + | | | of the Sickle + ----------------+---------------+-------------+-------------------------- + +The five stars marked * belong to the Southern hemisphere, and we can +never see them unless we travel far south. Last winter I went to Florida +and saw Canopus, but to see the Southern Cross you should cross the +Tropic of Cancer. + + + + +HOW TO LEARN MORE + + +All I can hope to do in this book is to get you enthusiastic about +astronomy. I don't mean "gushy." Look in the dictionary and you will +find that the enthusiast is not the faddist. He is the one who sticks to +a subject for a lifetime. + +Nor do I care a rap whether you become an astronomer--or even buy a +telescope. There will be always astronomers coming on, but there are too +few people who know and love even a few of the stars. I want you to make +popular astronomy a life-long hobby. Perhaps you may have to drop it for +ten or fifteen years. Never mind, you will take up the study again. I +can't expect you to read a book on stars if you are fighting to make a +living or support a family, unless it really rests you to read about the +stars. It does rest me. When things go wrong at the office or at home, I +can generally find rest and comfort from music. And if the sky is clear, +I can look at the stars, and my cares suddenly seem small and drop away. + +Let me tell you why and how you can get the very best the stars have to +teach you, without mathematics or telescope. Follow this programme and +you need never be afraid of hard work, or of exhausting the pleasures +of the subject. Go to your public library and get one of the books I +recommend in this chapter, and read whatever interests you. I don't care +whether you take up planets before comets or comets before planets, but +whatever you do do it well. Soak the interesting facts right in. Nail +them down. See everything the book talks about. Make notes of things to +watch for. Get a little blank book and write down the date you first saw +each thing of interest. Write down the names of the constellations you +love most. Before you lay down any star book you are reading, jot down +the most wonderful and inspiring thing you have read--even if you have +only time to write a single word that may recall it all to you. Treasure +that little note book as long as you live. Every year it will get more +precious to you. + +Now for the books: + +1. _Martin._ _The Friendly Stars._ Harper & Brothers, New York, 1907. + +This book teaches you first the twenty brightest stars and then the +constellations. I cannot say that this, or any other, is the "best +book," but it has helped me most, and I suppose it is only natural that +we should love best the first book that introduces us to a delightful +subject. + +2. _Serviss._ _Astronomy with the Naked Eye._ Harper & Brothers, New +York, 1908. + +This teaches you the constellations first and the brightest stars +incidentally. Also it gives the old myths. + +3. _Serviss._ _Astronomy with an Opera-Glass._ D. Appleton & Co., New +York, 1906. + +4. _Serviss._ _Pleasures of the Telescope._ D. Appleton & Co., New York, +1905. + +5. _Milham._ _How to Identify the Stars._ The Macmillan Co., New York, +1909. + +This gives a list of eighty-eight constellations, including thirty-six +southern ones, and has tracings of twenty-eight. + +6. _Elson._ _Star Gazer's Handbook._ Sturgis & Walton Co., New York, +1909. + +About the briefest and cheapest. Has good charts and makes a specialty +of the myths. + +7. _Serviss._ _Curiosities of the Sky._ Harper & Brothers, New York. + +Tells about comets, asteroids, shooting stars, life on Mars, nebulae, +temporary stars, coal-sacks, Milky Way, and other wonders. + +8. _Ball._ _Starland._ Ginn & Co., Boston, New York, etc., 1899. + +This tells about a great many interesting experiments in astronomy that +children can make. + + * * * * * + +If I had only a dollar or less to spend on astronomy I should buy a +planisphere. I got mine from Thomas Whittaker, No. 2 Bible House, New +York. It cost seventy-five cents, and will tell you where to find any +star at any time in the year. It does not show the planets, however. A +planisphere that will show the planets costs about five dollars. +However, there are only two very showy planets, viz., Venus and Jupiter. +Any almanac will tell you (for nothing) when each of these is morning +star, and when each of them is evening star. + +The best newspaper about stars, as far as I know, is a magazine called +_The Monthly Evening Sky Map_, published by Leon Barritt, 150 Nassau +St., New York. It costs a dollar a year. It gives a chart every month, +showing all the planets, and all the constellations. Also it tells you +about the interesting things, like comets, before they come. + +Good-bye. I hope you will never cease to learn about and love the earth +and the sky. Perhaps you think you have learned a great deal already. +But your pleasures have only begun. Wait till you learn about how the +world began, the sun and all his planets, the distances between the +stars, and the millions of blazing suns amid the Milky Way! + + +THE END + +[Illustration: THE SKY IN WINTER] + +NOTE.--These simplified star maps are not as accurate as a planisphere, +but they may be easier for children. All star maps are like ordinary +maps, except that east and west are transposed. The reason for this is +that you can hold a star map over your head, with the pole star toward +the north, and the map will then match the sky. These maps contain some +constellations that are only for grown-ups to study. The Winter +constellations every child should know are: + + AURIGA, the Charioteer + CANIS MAJOR, the Big Dog + CANIS MINOR, the Little Dog + CASSIOPEIA, the Queen in Her Chair + CYGNUS, the Swan + LEO, the Lion + ORION, the Hunter + PERSEUS, Which Has the Arc + TAURUS, the Bull + URSA MAJOR, the Great Bear + URSA MINOR, the Little Bear + +[Illustration: THE SKY IN SPRING] + +NOTE.--Once upon a time all the educated people spoke Latin. It was the +nearest approach to a universal language. So most of the constellations +have Latin names. The English, French and German names are all +different, but if all children would learn the Latin names they could +understand one another. The Spring constellations every child should +know are: + + LEO, the Lion + LYRA, the Lyre + CASSIOPEIA, the Queen in her Chair + SCORPIO, the Scorpion + URSA MAJOR, the Great Bear + URSA MINOR, the Little Bear + VIRGO, the Virgin + +[Illustration: THE SKY IN SUMMER] + +NOTE.--Every sky map is good for three months, in this way: If this is +correct on June 1st at 10 P.M., it will be correct July 1st at 8 P.M., +and August 1st at 6 P.M. This is because the stars rise four minutes +earlier every night. Thus, after thirty days, any star will rise thirty +times four minutes earlier, or 120 minutes, or two hours. Children need +not learn all the Summer constellations. The most interesting are: + + AURIGA, the Charioteer + CANIS MAJOR, the Big Dog + CYGNUS, the Swan + LYRA, the Lyre + SCORPIO, the Scorpion + +[Illustration: THE SKY IN AUTUMN] + +NOTE.--This book tells how to find all the most interesting stars and +constellations without maps, but many people prefer them. How to use +star maps is explained under "The Sky in Winter." The Autumn +constellations most interesting to children are: + + AQUILA, the Eagle + AURIGA, the Charioteer + CASSIOPEIA, the Queen in Her Chair + CYGNUS, the Swan + LYRA, the Lyre + PERSEUS, Which Has the Arc + TAURUS, the Bull + URSA MAJOR, the Great Bear + URSA MINOR, the Little Bear + + +Transcriber's notes + + Page 124 "streams, runing" corrected to "streams, running" + Page 127 "where he globe" corrected to "where the globe" + Page 138 "ceatures to prove" corrected to "creatures to prove" + Page 216 "this consellation is" corrected to "this constellation is" + Page 203 "Everybirth day" corrected to "Every birthday" + + + + + + + +End of the Project Gutenberg EBook of Earth and Sky Every Child Should Know, by +Julia Ellen Rogers + +*** END OF THIS PROJECT GUTENBERG EBOOK EARTH AND SKY *** + +***** This file should be named 32598.txt or 32598.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/3/2/5/9/32598/ + +Produced by Juliet Sutherland, Christine D. and the Online +Distributed Proofreading Team at http://www.pgdp.net + + +Updated editions will replace the previous one--the old editions +will be renamed. + +Creating the works from public domain print editions means that no +one owns a United States copyright in these works, so the Foundation +(and you!) can copy and distribute it in the United States without +permission and without paying copyright royalties. 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