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diff --git a/2937.txt b/2937.txt new file mode 100644 index 0000000..5a994dc --- /dev/null +++ b/2937.txt @@ -0,0 +1,968 @@ +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 + +Posting Date: January 6, 2009 [EBook #2937] +Release Date: November, 2001 + +Language: English + +Character set encoding: ASCII + +*** START OF THIS PROJECT GUTENBERG EBOOK CORAL AND CORAL REEFS *** + + + + +Produced by Amy E. Zelmer + + + + + +CORAL AND CORAL REEFS + +by Thomas H. Huxley + +[1] + + +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. + +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. + +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. + +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. + +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. + +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. + +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. + +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. + +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. + +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. + +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." + +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. + +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. + +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. + +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. + +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. + + + +[Footnote 1: A Lecture delivered in Manchester, November 4th, 1870.] + + + + + +End of Project Gutenberg's Coral and Coral Reefs, by Thomas H. Huxley + +*** END OF THIS PROJECT GUTENBERG EBOOK CORAL AND CORAL REEFS *** + +***** This file should be named 2937.txt or 2937.zip ***** +This and all associated files of various formats will be found in: + http://www.gutenberg.org/2/9/3/2937/ + +Produced by Amy E. 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