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diff --git a/2937-h/2937-h.htm b/2937-h/2937-h.htm new file mode 100644 index 0000000..24c1e33 --- /dev/null +++ b/2937-h/2937-h.htm @@ -0,0 +1,1041 @@ +<?xml version="1.0" encoding="us-ascii"?> + +<!DOCTYPE html + PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" + "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd" > + +<html xmlns="http://www.w3.org/1999/xhtml" lang="en"> + <head> + <title> + Coral and Coral Reefs, by Thomas H. Huxley + </title> + <style type="text/css" xml:space="preserve"> + + body { margin:5%; background:#faebd0; text-align:justify} + P { text-indent: 1em; margin-top: .25em; margin-bottom: .25em; } + H1,H2,H3,H4,H5,H6 { text-align: center; margin-left: 15%; margin-right: 15%; } + hr { width: 50%; text-align: center;} + .foot { margin-left: 20%; margin-right: 20%; text-align: justify; text-indent: -3em; font-size: 90%; } + blockquote {font-size: 97%; font-style: italic; margin-left: 10%; margin-right: 10%;} + .mynote {background-color: #DDE; color: #000; padding: .5em; margin-left: 10%; margin-right: 10%; font-family: sans-serif; font-size: 95%;} + .toc { margin-left: 10%; margin-bottom: .75em;} + .toc2 { margin-left: 20%;} + div.fig { display:block; margin:0 auto; text-align:center; } + div.middle { margin-left: 20%; margin-right: 20%; text-align: justify; } + .figleft {float: left; margin-left: 0%; margin-right: 1%;} + .figright {float: right; margin-right: 0%; margin-left: 1%;} + .pagenum {display:inline; font-size: 70%; font-style:normal; + margin: 0; padding: 0; position: absolute; right: 1%; + text-align: right;} + pre { font-style: italic; font-size: 90%; margin-left: 10%;} + +</style> + </head> + <body> +<pre xml:space="preserve"> + +The Project Gutenberg EBook of Coral and Coral Reefs, by Thomas H. Huxley + +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: Coral and Coral Reefs + +Author: Thomas H. Huxley + +Release Date: January 6, 2009 [EBook #2937] +Last Updated: January 22, 2013 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK CORAL AND CORAL REEFS *** + + + + +Produced by Amy E. Zelmer, and David Widger + + + + + + +</pre> + <p> + <br /><br /> + </p> + <h1> + CORAL AND CORAL REEFS + </h1> + <p> + <br /> + </p> + <h2> + by Thomas H. Huxley + </h2> + <p> + <br /> <a href="#linknote-1" name="linknoteref-1" id="linknoteref-1"><small>[1]</small></a> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> + </p> + <p> + THE subject upon which I wish to address you to-night is the structure and + origin of Coral and Coral Reefs. Under the head of "coral" there are + included two very different things; one of them is that substance which I + imagine a great number of us have champed when we were very much younger + than we are now,—the common red coral, which is used so much, as you + know, for the edification and the delectation of children of tender years, + and is also employed for the purposes of ornament for those who are much + older, and as some think might know better. The other kind of coral is a + very different substance; it may for distinction's sake be called the + white coral; it is a material which most assuredly not the hardest-hearted + of baby farmers would give to a baby to chew, and it is a substance which + is to be seen only in the cabinets of curious persons, or in museums, or, + may be, over the mantelpieces of sea-faring men. But although the red + coral, as I have mentioned to you, has access to the very best society; + and although the white coral is comparatively a despised product, yet in + this, as in many other cases, the humbler thing is in reality the greater; + the amount of work which is done in the world by the white coral being + absolutely infinite compared with that effected by its delicate and + pampered namesake. Each of these substances, the white coral and the red, + however, has a relationship to the other. They are, in a zoological sense, + cousins, each of them being formed by the same kind of animals in what is + substantially the same way. Each of these bodies is, in fact, the hard + skeleton of a very curious and a very simple animal, more comparable to + the bones of such animals as ourselves than to the shells of oysters or + creatures of that kind; for it is the hardening of the internal tissue of + the creature, of its internal substance, by the deposit in the body of a + material which is exceedingly common, not only in fresh but in sea water, + and which is specially abundant in those waters which we know as "hard," + those waters, for example, which leave a "fur" upon the bottom of a + tea-kettle. This "fur" is carbonate of lime, the same sort of substance as + limestone and chalk. That material is contained in solution in sea water, + and it is out of the sea water in which these coral creatures live that + they get the lime which is needed for the forming of their hard skeleton. + </p> + <p> + But now what manner of creatures are these which form these hard + skeletons? I dare say that in these days of keeping aquaria, of locomotion + to the sea-side, most of those whom I am addressing may have seen one of + those creatures which used to be known as the "sea anemone," receiving + that name on account of its general resemblance, in a rough sort of way, + to the flower which is known as the "anemone"; but being a thing which + lives in the sea, it was qualified as the "sea anemone." Well, then, you + must suppose a body shaped like a short cylinder, the top cut off, and in + the top a hole rather oval than round. All round this aperture, which is + the mouth, imagine that there are placed a number of feelers forming a + circle. The cavity of the mouth leads into a sort of stomach, which is + very unlike those of the higher animals, in the circumstance that it opens + at the lower end into a cavity of the body, and all the digested matter, + converted into nourishment, is thus distributed through the rest of the + body. That is the general structure of one of these sea anemones. If you + touch it it contracts immediately into a heap. It looks at first quite + like a flower in the sea, but if you touch it you find that it exhibits + all the peculiarities of a living animal; and if anything which can serve + as its prey comes near its tentacles, it closes them round it and sucks + the material into its stomach and there digests it and turns it to the + account of its own body. + </p> + <p> + These creatures are very voracious, and not at all particular what they + seize; and sometimes it may be that they lay hold of a shellfish which is + far too big to be packed into that interior cavity, and, of course, in any + ordinary animal a proceeding of this kind would give rise to a very severe + fit of indigestion. But this is by no means the case in the sea anemone, + because when digestive difficulties of this kind arise he gets out of them + by splitting himself in two; and then each half builds itself up into a + fresh creature, and you have two polypes where there was previously one, + and the bone which stuck in the way lying between them! Not only can these + creatures multiply in this fashion, but they can multiply by buds. A bud + will grow out of the side of the body (I am not speaking of the common sea + anemone, but of allied creatures) just like the bud of a plant, and that + will fashion itself into a creature just like the parent. There are some + of them in which these buds remain connected together, and you will soon + see what would be the result of that. If I make a bud grow out here, and + another on the opposite side, and each fashions itself into a new polype, + the practical effect will be that before long you will see a single polype + converted into a sort of tree or bush of polypes. And these will all + remain associated together, like a kind of co-operative store, which is a + thing I believe you understand very well here,—each mouth will help + to feed the body and each part of the body help to support the + multifarious mouths. I think that is as good an example of a zoological + co-operative store as you can well have. Such are these wonderful + creatures. But they are capable not only of multiplying in this way, but + in other ways, by having a more ordinary and regular kind of offspring. + Little eggs are hatched and the young are passed out by the way of the + mouth, and they go swimming about as little oval bodies covered with a + very curious kind of hairlike processes. Each of these processes is + capable of striking water like an oar; and the consequence is that the + young creature is propelled through the water. So that you have the young + polype floating about in this fashion, covered by its 'vibratile cilia', + as these long filaments, which are capable of vibration are termed. And + thus, although the polype itself may be a fixed creature unable to move + about, it is able to spread its offspring over great areas. For these + creatures not only propel themselves, but while swimming about in the sea + for many hours, or perhaps days, it will be obvious that they must be + carried hither and thither by the currents of the sea, which not + unfrequently move at the rate of one or two miles an hour. Thus, in the + course of a few days, the offspring of this stationary creature may be + carried to a very great distance from its parent; and having been so + carried it loses these organs by which it is propelled, and settles down + upon the bottom of the sea and grows up again into the form and condition + of its parents. So that if you suppose a single polype of this kind + settled upon the bottom of the sea, it may by these various methods—that + is to say, by cutting itself in two, which we call "fission," or by + budding; or by sending out these swimming embryos,—multiply itself + to an enormous extent, and give rise to thousands, or millions, of progeny + in a comparatively short time; and these thousands, or millions, of + progeny may cover a very large surface of the sea bottom; in fact, you + will readily perceive that, give them time, and there is no limit to the + surface which they may cover. + </p> + <p> + Having understood thus far the general nature of these polypes, which are + the fabricators both of the red and white coral, let us consider a little + more particularly how the skeletons of the red coral and of the white + coral are formed. The red coral polype perches upon the sea bottom, it + then grows up into a sort of stem, and out of that stem there grow + branches, each of which has its own polypes; and thus you have a kind of + tree formed, every branch of the tree terminated by its polype. It is a + tree, but at the end of the branches there are open mouths of polypes + instead of flowers. Thus there is a common soft body connecting the whole, + and as it grows up the soft body deposits in its interior a quantity of + carbonate of lime, which acquires a beautiful red or flesh colour, and + forms a kind of stem running through the whole, and it is that stem which + is the red coral. The red coral grows principally at the bottom of the + Mediterranean Sea, at very great depths, and the coral fishers, who are + very adventurous seamen, take their drag nets, of a peculiar kind, roughly + made, but efficient for their purpose, and drag them along the bottom of + the sea to catch the branches of the red coral, which become entangled and + are thus brought up to the surface. They are then allowed to putrefy, in + order to get rid of the animal matter, and the red coral is the skeleton + that is left. + </p> + <p> + In the case of the white coral, the skeleton is more complete. In the red + coral, the skeleton belongs to the whole; in the white coral there is a + special skeleton for every one of these polypes in addition to that for + the whole body. There is a skeleton formed in the body of each of them, + like a cup divided by a number of radiating partitions towards the + outside; and that cup is formed of carbonate of lime, only not stained + red, as in the case of the red coral. And all these cups are joined + together into a common branch, the result of which is the formation of a + beautiful coral tree. This is a great mass of madrepore, and in the living + state every one of the ends of these branches was terminated by a + beautiful little polype, like a sea anemone, and all the skeleton was + covered by a soft body which united the polypes together. You must + understand that all this skeleton has been formed in the interior of the + body, to suit the branched body of the polype mass, and that it is as much + its skeleton as our own bones are our skeleton. In this next coral the + creature which has formed the skeleton has divided itself as it grew, and + consequently has formed a great expansion; but scattered all over this + surface there were polype bodies like those I previously described. Again, + when this great cup was alive, the whole surface was covered with a + beautiful body upon which were set innumerable small polype flowers, if we + may so call them, often brilliantly coloured; and the whole cup was built + up in the same fashion by the deposit of carbonate of lime in the interior + of the combined polype body, formed by budding and by fission in the way I + described. You will perceive that there is no necessary limit to this + process. There is no reason why we should not have coral three or four + times as big; and there are certain creatures of this kind that do + fabricate very large masses, or half spheres several feet in diameter. + Thus the activity of these animals in separating carbonate of lime from + the sea and building it up into definite shapes is very considerable + indeed. + </p> + <p> + Now I think I have said sufficient—as much as I can without taking + you into technical details, of the general nature of these creatures which + form coral. The animals which form coral are scattered over the seas of + all countries in the world. The red coral is comparatively limited, but + the polypes which form the white coral are widely scattered. There are + some of them which remain single, or which give rise to only small + accumulations; and the skeletons of these, as they die, accumulate upon + the bottom of the sea, but they do not come to much; they are washed about + and do not adhere together, but become mixed up with the mud of the sea. + But there are certain parts of the world in which the coral polypes which + live and grow are of a kind which remain, adhere together, and form great + masses. They differ from the ordinary polypes just in the same way as + those plants which form a peat-bog or meadow-turf differ from ordinary + plants. They have a habit of growing together in masses in the same place; + they are what we call "gregarious" things; and the consequence of this is, + that as they die and leave their skeletons, those skeletons form a + considerable solid aggregation at the bottom of the sea, and other polypes + perch upon them, and begin building upon them, and so by degrees a great + mass is formed. And just as we know there are some ancient cities in which + you have a British city, and over that the foundations of a Roman city; + and over that a Saxon city, and over that again a modern city, so in these + localities of which I am speaking, you have the accumulations of the + foundations of the houses, if I may use the term, of nation after nation + of these coral polypes; and these accumulations may cover a very + considerable space, and may rise in the course of time from the bottom to + the surface of the sea. + </p> + <p> + Mariners have a name which they apply to all sorts of obstacles consisting + of hard and rocky matter which comes in their way in the course of their + navigation; they call such obstacles "reefs," and they have long been in + the habit of calling the particular kind of reef, which is formed by the + accumulation of the skeletons of dead corals, by the name of "coral + reefs," therefore, those parts of the world in which these accumulations + occur have been termed by them "coral reef areas," or regions in which + coral reefs are found. There is a very notable example of a simple coral + reef about the island of Mauritius, which I dare say you all know, lies in + the middle of the Indian Ocean. It is a very considerable and beautiful + island, and is surrounded on all sides by a mass of coral, which has been + formed in the way I have described; so that if you could get upon the top + of one of the peaks of the island, and look down upon the Indian Ocean, + you would see that the beach round the Island was continued outward by a + kind of shallow terrace, which is covered by the sea, and where the sea is + quite shallow; and at a distance varying from three-quarters of a mile to + a mile and a half from the proper beach, you would see a line of foam or + surf which looks most beautiful in contrast with the bright green water in + the inside, and the deep blue of the sea beyond. That line of surf + indicates the point at which the waters of the ocean are breaking upon the + coral reef which surrounds the island. You see it sweep round the island + upon all sides, except where a river may chance to come down, and that + always makes a gap in the shore. + </p> + <p> + There are two or three points which I wish to bring clearly before your + notice about such a reef as this. In the first place, you perceive it + forms a kind of fringe round the island, and is therefore called a + "fringing reef." In the next place, if you go out in a boat, and take + soundings at the edge of the reef, you find that the depth of the water is + not more than from 20 to 25 fathoms—that is about 120 to 150 feet. + Outside that point you come to the natural sea bottom; but all inside that + depth is coral, built up from the bottom by the accumulation of the + skeletons of innumerable generations of coral polypes. So that you see the + coral forms a very considerable rampart round the island. What the exact + circumference may be I do not remember, but it cannot be less than 100 + miles, and the outward height of this wall of coral rock nowhere amounts + to less than about 100 or 150 feet. + </p> + <p> + When the outward face of the reef is examined, you find that the upper + edge, which is exposed to the wash of the sea, and all the seaward face, + is covered with those living plant-like flowers which I have described to + you. They are the coral polypes which grow, flourish, and add to the mass + of calcareous matter which already forms the reef. But towards the lower + part of the reef, at a depth of about 120 feet, these creatures are less + active, and fewer of them at work; and at greater depths than that you + find no living coral polype at all; and it may be laid down as a rule, + derived from very extensive observation, that these reef-building corals + cannot live in a greater depth of water than about 120 to 150 feet. I beg + you to recollect that fact, because it is one I shall have to come back to + by and by, and to show to what very curious consequences that rule leads. + Well then, coming back to the margin of the reef, you find that part of it + which lies just within the surf to be coated by a very curious plant, a + sort of seaweed, which contains in its substance a very great deal of + carbonate of lime, and looks almost like rock; this is what is called the + nulli pore. More towards the land, we come to the shallow water upon the + inside of the reef, which has a particular name, derived from the Spanish + or the Portuguese—it is called a "lagoon," or lake. In this lagoon + there is comparatively little living coral; the bottom of it is formed of + coral mud. If we pounded this coral in water, it would be converted into + calcareous mud, and the waves during storms do for the coral skeletons + exactly what we might do for this coral in a mortar; the waves tear off + great fragments and crush them with prodigious force, until they are + ground into the merest powder, and that powder is washed into the interior + of the lagoon, and forms a muddy coating at the bottom. Beside that there + are a great many animals that prey upon the coral—fishes, worms, and + creatures of that kind, and all these, by their digestive processes, + reduce the coral to the same state, and contribute a very important + element to this fine mud. The living coral found in the lagoon, is not the + reef building coral; it does not give rise to the same massive skeletons. + As you go in a boat over these shallow pools, you see these beautiful + things, coloured red, blue, green, and all colours, building their houses; + but these are mere tenements, and not to be compared in magnitude and + importance to the masses which are built by the reef-builders themselves. + Now such a structure as this is what is termed a "fringing reef." You meet + with fringing reefs of this kind not only in the Mauritius, but in a + number of other parts of the world. If these were the only reefs to be + seen anywhere, the problem of the formation of coral reefs would never + have been a difficult one. Nothing can be easier than to understand how + there must have been a time when the coral polypes came and settled on the + shores of this island, everywhere within the 20 to 25 fathom line, and + how, having perched there, they gradually grew until they built up the + reef. + </p> + <p> + But these are by no means the only sort of coral reefs in the world; on + the contrary, there are very large areas, not only of the Indian ocean, + but of the Pacific, in which many many thousands of square miles are + covered either with a peculiar kind of reef, which is called the + "encircling reef," or by a still more curious reef which goes by the name + of the "atoll." There is a very good picture, which Professor Roscoe has + been kind enough to prepare for me, of one of these atolls, which will + enable you to form a notion of it as a landscape. You have in the + foreground the waters of the Pacific. You must fancy yourself in the + middle of the great ocean, and you will perceive that there is an almost + circular island, with a low beach, which is formed entirely of coral sand; + growing upon that beach you have vegetation, which takes, of course, the + shape of the circular land; and then, in the interior of the circle, there + is a pool of water, which is not very deep—probably in this case not + more than eight or nine fathoms—and which forms a strange and + beautiful contrast to the deep blue water outside. This circular island, + or atoll, with a lagoon in the middle, is not a complete circle; upon one + side of it there is a break, exactly like the entrance into a dock; and, + as a matter of course, these circular islets, or atolls, form most + efficient break-waters, for if you can only get inside your ship is in + perfect safety, with admirable anchorage in the interior. If the ship were + lying within a mile of that beach, the water would be one or two thousand + feet deep; therefore, a section of that atoll, with the soundings as deep + as this all round, would give you the notion of a great cone, cut off at + the top, and with a shallow cup in the middle of it. Now, what a very + singular fact this is, that we should have rising from the bottom of the + deep ocean a great pyramid, beside which all human pyramids sink into the + most utter insignificance! These singular coral limestone structures are + very beautiful, especially when crowned with cocoa-nut trees. There you + see the long line of land, covered with vegetation—cocoa-nut trees—and + you have the sea upon the inner and outer sides, with a vessel very + comfortably riding at anchor. That is one of the remarkable forms of reef + in the Pacific. Another is a sort of half-way house, between the atoll and + the fringing reef; it is what is called an "encircling reef." In this case + you see an Island rising out of the sea, and at two or three miles + distance, or more, and separated by a deep channel, which may be eight to + twelve fathoms deep, there is a reef, which encircles it like a great + girdle; and outside that again the water is one or two thousand feet deep. + I spent three or four years of my life in cruising about a modification of + one of these encircling reefs, called a "barrier reef," upon the east + coast of Australia—one of the most wonderful accumulations of coral + rock in the world. It is about 1,100 miles long, and varies in width from + one or two to many miles. It is separated from the coast of Australia by a + channel of about 25 fathoms deep; while outside, looking toward America, + the water is two or three thousand feet deep at a mile from the edge of + the reef. This is an accumulation of limestone rock, built up by corals, + to which we have no parallel anywhere else. Imagine to yourself a heap of + this material more than one thousand miles long, and several miles wide. + That is a barrier reef; but a barrier reef is merely as it were a fragment + of an encircling reef running parallel to the coast of a great continent. + </p> + <p> + I told you that the polypes which built these reefs were not able to live + at a greater depth than 20 to 25 fathoms of water; and that is the reason + why the fringing reef goes no farther from the land than it does. And for + the same reason, if the Pacific could be laid bare we should have a most + singular spectacle. There would be a number of mountains with truncated + tops scattered over it, and those mountains would have an appearance just + the very reverse of that presented by the mountains we see on shore. You + know that the mountains on shore are covered with vegetation at their + bases, while their tops are barren or covered with snow; but these + mountains would be perfectly bare at their bases, and all round their tops + they would be covered with a beautiful vegetation of coral polypes. And + not only would this be the case, but we should find that for a + considerable distance down, all the material of these atoll and encircling + reefs was built up of precisely the same coral rock as the fringing reef. + That is to say, you have an enormous mass of coral rock at a depth below + the surface of the water where we know perfectly well that the coral + animals could not have lived to form it. When those two facts were first + put together, naturalists were quite as much puzzled as I daresay you are, + at present, to understand how these two seeming contradictions could be + reconciled; and all sorts of odd hypotheses were resorted to. It was + supposed that the coral did not extend so far down, but that there was a + great chain of submarine mountains stretching through the Pacific, and + that the coral had grown upon them. But only fancy what supposition that + was, for you would have to imagine that there was a chain of mountains a + thousand miles or more long, and that the top of every mountain came + within 20 fathoms of the surface of the sea, and neither rose above nor + sunk beneath that level. That is highly improbable: such a chain of + mountains was never known. Then how can you possibly account for the + curious circular form of the atolls by any supposition of this kind? I + believe there was some one who imagined that all these mountains were + volcanoes, and that the reefs had grown round the tops of the craters, so + we all stuck fast. I may say "we," though it was rather before my time. + And when we all stick fast, it is just the use of a man of genius that he + comes and shows us the meaning of the thing. He generally gives an + explanation which is so ridiculously simple that everybody is ashamed that + he did not find it out before; and the way such a discoverer is often + rewarded is by finding out that some one had made the discovery before + him! I do not mean to say that it was so in this particular instance, + because the great man who played the part of Columbus and the egg on this + occasion had, I believe, always had the full credit which he so well + deserves. The discoverer of the key to these problems was a man whose name + you know very well in connection with other matters, and I should not + wonder if some of you have heard it said that he was a superficial kind of + person who did not know much about the subject on which he writes. He was + Mr. Darwin, and this brilliant discovery of his was made public thirty + years ago, long before he became the celebrated man he now is; and it was + one of the most singular instances of that astonishing sagacity which he + possesses of drawing consequences by way of deduction from simple + principles of natural science—a power which has served him in good + stead on other occasions. Well, Mr. Darwin, looking at these curious + difficulties and having that sort of knowledge of natural phenomena in + general, without which he could not have made a step towards the solution + of the problem, said to himself—"It is perfectly clear that the + coral which forms the base of the atolls and fringing reefs could not + possibly have been formed there if the level of the sea has always been + exactly where it is now, for we know for certain that these polypes cannot + build at a greater depth than 20 to 25 fathoms, and here we find them at + 50 to 100 fathoms." + </p> + <p> + That was the first point to make clear. The second point to deal with was—if + the polypes cannot have built there while the level of the sea has + remained stationary, then one of two things must have happened—either + the sea has gone up, or the land has gone down. + </p> + <p> + There is no escape from one of these two alternatives. Now the objections + to the notion of the sea having gone up are very considerable indeed; for + you will readily perceive that the sea could not possibly have risen a + thousand feet in the Pacific without rising pretty much the same distance + everywhere else; and if it had risen that height everywhere else since the + reefs began to be formed, the geography of the world in general must have + been very different indeed, at that time, from what it is now. And we have + very good means of knowing that any such rise as this certainly has not + taken place in the level of the sea since the time that the corals have + been building their houses. And so the only other alternative was to + suppose that the land had gone down, and at so slow a rate that the corals + were able to grow upward as fast as it went downward. You will see at once + that this is the solution of the mystery, and nothing can be simpler or + more obvious when you come to think about it. Suppose we start with a + coral sea and put in the middle of it an island such as the Mauritius. Now + let the coral polypes come and perch on the shore and build a fringing + reef, which will stop when they come to 20 or 25 fathoms, and you will + have a fringing reef like that round the island in the illustration. So + long as the land remains stationary, so long as it does not descend so + long will that reef be unable to get any further out, because the moment + the polype embryos try to get below they die. But now suppose that the + land sinks very gradually indeed. Let it subside by slow degrees, until + the mountain peak, which we have in the middle of it, alone projects + beyond the sea level. The fringing reef would be carried down also; but we + suppose that the sinking is so slow that the coral polypes are able to + grow up as fast as the land is carried down; consequently they will add + layer upon layer until they form a deep cup, because the inner part of the + reef grows much more slowly than the outer part. Thus you have the reef + forming a bed thicker upon the flanks of the island; but the edge of the + reef will be very much further out from the land, and the lagoon will be + many times deeper; in short, your fringing reef will be converted into an + encircling reef. And if, instead of this being an island, it were a great + continent like Australia, then you will have the phenomenon of a barrier + reef which I have described. The barrier reef of Australia was originally + a fringing reef; the land has gone slowly down; the consequence is the + lagoon has deepened until its depth is now 25 fathoms and the corals have + grown up at the outer edge until you have that prodigious accumulation + which forms the barrier reef at present. Now let this process go on + further still; let us take the land a further step down, so as to submerge + even the peak. The coral, still growing up, will cover the surface of the + land, and you will have an atoll reef; that is to say, a more or less + circular or oval ring of coral rock with a lagoon in the middle. Thus you + see that every peculiarity and phenomenon of these different forms of + coral reef was explained at once by the simplest of all possible + suppositions, namely, by supposing that the land has gone down at a rate + not greater than that at which the coral polypes have grown up. You + explain a Fringing Reef as a reef which is formed round land comparatively + stationary; an Encircling Reef as one which is formed round land going + down; and an Atoll as a reef formed upon land gone down; and the thing is + so simple that a child may understand it when it is once explained. + </p> + <p> + But this would by no means satisfy the conditions of a scientific + hypothesis. No man who is cautious would dream of trusting to an + explanation of this kind simply because it explained one particular set of + facts. Before you can possibly be safe in dealing with Nature—who is + very properly made of the feminine gender, on account of the astonishing + tricks which she plays upon her admirers!—I say before you can be + safe in dealing with Nature, you must get two or three kinds of cross + proofs, so as to make sure not only that your hypothesis fits that + particular set of facts, but that it is not contradicted by some other set + of facts which is just as clear and certain. And it so happens, that in + this case Mr. Darwin supplied the cross proofs as well as the immediate + evidence. You have all heard of volcanoes, those wonderful vents in the + surface of the earth out of which pour masses of lava, cinders and ashes, + and the like. Now, it is a matter of observation and experience that all + volcanoes are placed in areas in which the surface of the earth is + undergoing elevation, or at any rate is stationary; they are not placed in + parts of the world in which the level of the land is being lowered. They + are all indications of a great subterranean activity, of a something being + pushed up, and therefore naturally the land either gives way and lets it + come through, or else is raised up by its violence. And so Mr. Darwin, + being desirous not to merely put out a flashy hypothesis, but to get at + the truth of the matter, said to himself, "If my notion of this matter is + right, then atolls and encircling reefs, inasmuch as they are dependent + upon subsidence, ought not to be found in company with volcanoes; and, + 'vice versa', volcanoes ought not to be found in company with atolls, but + they ought to be found in company with fringing reefs." And if you turn to + Mr. Darwin's great work upon the coral reefs, you will see a very + beautiful chart of the world, which he prepared with great pains and + labour, showing the distribution on the one hand of the reefs, and on the + other of the volcanoes; you will find that in no case does the atoll + accompany the volcano, or the volcano burst up among the atolls. It is + most instructive to look at the great area of the Pacific on the map, and + see the great masses of atolls forming in one region of it a most enormous + belt, running from north-west to south-east; while the volcanoes, which + are very numerous in that region, go round the margin, so that we can + picture the Pacific to ourselves a section of a kind of very shallow basin—shallow + in proportion to its width, with the atolls rising from the bottom of it, + and at the margins the volcanoes. It is exactly as if you had taken a flat + mass and lifted up the edges of it; the subterranean force which lifted up + the edges shows itself in volcanoes, and as the edges have been raised, + the middle part of the mass has gone down. In other words, the facts of + physical geography precisely and exactly correspond with the hypothesis + which accounts for the infinite varieties of coral reefs. + </p> + <p> + One other point, before I conclude, about this matter. These reefs, as you + have just perceived, are in a most singular and unexpected manner + indications of physical changes of elevations and depressions going on + upon the surface of the globe. I dare say it may have surprised you to + hear me talk in this familiar sort of way of land going up and down; but + it is one of the universal lessons of geology that the land is going down + and going up, and has been going up and down, in all sorts of places and + to all sorts of distances, through all recorded time. Geologists would be + quite right in maintaining the seeming paradox that the stable thing in + the world is the fluid sea and the shifting thing is the solid land. That + may sound a very hard saying at first, but the more you look into geology, + the more you will see ground for believing that it is not a mere paradox. + </p> + <p> + In an unexpected manner, again, these reefs afford us not only an + indication of change of place, but they afford an indication of lapse of + time. The reef is a timekeeper of a very curious character; and you can + easily understand why. The coral polype, like everything else, takes a + certain time to grow to its full size; it does not do it in a minute; just + as a child takes a certain time to grow into a man so does the embryo + polype take time to grow into a perfect polype and form its skeleton. + Consequently every particle of coral limestone is an expression of time. + It must have taken a certain time to separate the lime from the sea water. + It is not possible to arrive at an accurate computation of the time it + must have taken to form these coral islands, because we lack the necessary + data; but we can form a rough calculation, which leads to very curious and + striking results. The computations of the rate at which corals grow are so + exceedingly variable, that we must allow the widest possible margin for + error; and it is better in this case to make the allowance upon the side + of excess. I think that anybody who knows anything about the matter will + tell you that I am making a computation far in excess of what is probable, + if I say that an inch of coral limestone may be added to one of these + reefs in the course of a year. I think most naturalists would be inclined + to laugh at me for making such an assumption, and would put the growth at + certainly not more than half that amount. But supposing it is so, what a + very curious notion of the antiquity of some of these great living + pyramids comes out by a very simple calculation. There is no doubt + whatever that the sea faces of some of them are fully a thousand feet + high, and if you take the reckoning of an inch a year, that will give you + 12,000 years for the age of that particular pyramid or cone of coral + limestone; 12,000 long years have these creatures been labouring in + conditions which must have been substantially the same as they are now, + otherwise the polypes could not have continued their work. But I believe I + very much understate both the height of some of these masses, and + overstate the amount which these animals can form in the course of a year; + so that you might very safely double the period as the time during which + the Pacific Ocean, the general state of the climate, and the sea, and the + temperature has been substantially what it is now; and yet that state of + things which now obtains in the Pacific Ocean is the yesterday of the + history of the life of the globe. Those pyramids of coral rock are built + upon a foundation which is itself formed by the deposits which the + geologist has to deal with. If we go back in time and search through the + series of the rocks, we find at every age of the world's history which has + yet been examined, accumulations of limestone, many of which have + certainly been built up in just the same way as those coral reefs which + are now forming the bottom of the Pacific Ocean. And even if we turn to + the oldest periods of geologic history, although the nature of the + materials is changed, although we cannot apply to them the same reasonings + that we can to the existing corals, yet still there are vast masses of + limestone formed of nothing else than the accumulations of the skeletons + of similar animals, and testifying that even in those remote periods of + the world's history, as now, the order of things implies that the earth + had already endured for a period of which our ordinary standards of + chronology give us not the slightest conception. In other words, the + history of these coral reefs, traced out honestly and carefully, and with + the same sort of reasoning that you would use in the ordinary affairs of + life, testifies, like every fact that I know of, to the prodigious + antiquity of the earth since it existed in a condition in the main similar + to that in which it now is. + </p> + <p> + <br /> <br /> + </p> + <hr /> + <p> + <br /> <br /> <a name="linknote-1" id="linknote-1"> + <!-- Note --></a> + </p> + <p class="foot"> + 1 (<a href="#linknoteref-1">return</a>)<br /> [ A Lecture delivered in + Manchester, November 4th, 1870.] + </p> + <p> + <br /><br /><br /><br /> + </p> +<pre xml:space="preserve"> + + + + + +End of Project Gutenberg's Coral and Coral Reefs, by Thomas H. 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