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more we know of its structure and of the shapes? Extreme cases of any peculiar nature of its builder. But let the growth | phenomenon are always those which most of corals in seas of a certain depth and attract attention, and sometimes they are temperature be assumed and passed over, the cases which most readily suggest as we do assume and pass over a thousand an explanation. Ring-shaped islands of other things with which we are familiar. such moderate dimensions that the whole The puzzle here is why it should grow in of them can be taken in by the eye, supply the form of a linear barrier along a coast, such cases. There are atoll islands where and yet not touching it, but at a distance ships can enter, through some break in the more or less great-sometimes very great ring, into the inner circle. They find themand always leaving between it and the selves in a perfect harbor, in a sheltered land an enclosed and protected space of lake which no wave can ever enter, yet deep water, which, once they have found an enough and wide enough to hold all the entrance through the reef, ships can navi- navies of the world. Round about on every gate for hundreds of miles. Why should side there are the dazzling beaches which this same curious phenomenon be re- are composed of coral sand, and crowning peated on a smaller scale throughout the these there is the peaceful cocoanut palm, thousands of islands and islets which dot and a lower jungle of dense tropical vegethe immense surfaces of the Pacific? Why tation. On landing and exploring the should these islands so often be the centre woods and shores nothing can be seen but of a double ring- - first a ring of calm and coral. The whole island is a ring of this as it were inland water, then a ring of purely marine product; with the exception coral reef fronting the outer sea, and of an occasional fragment of pumice-stone, lastly the ocean, depths out of which the which having been floated over the sea coral reef rises like a wall? Why should from some distant volcanic eruption, like this curious arrangement repeat itself in that of Krakatoa, here disintegrates and every variety of form over thousands of furnishes clay, the most essential element miles until we come to that extreme case of a soil. But reason tells us that there when there is no island at all except the must be something else underground, howouter ring of the coral reef and an inner ever deeply buried. When the corals first pool or lake of shallower water which is began to grow, they must have found some thus secluded from the ocean, with noth-rock to build upon, and the shape of these ing to break its surface- shining with a walls must be the shape which was thus calm, splendid, and luminous green, set determined. One suggestion is obvious. off against the deep purple blues of the Elsewhere all over the globe there is only surrounding sea? For effects so uniform one physical cause which determines or so analogous, repeated and multiplied rocky matter into such ring-like forms as over an area so immense, there must be these, and which determines also an some physical cause as peculiar as its included space of depth more or less effects. Moreover, this cause must be profound. This physical cause is the one affecting not merely or only the pecul- eruptive action of volcanic force. When iarities of the animal which builds up the anchored in the central lagoon of a coral coral, but some cause affecting also the atoll, are we not simply anchored in the solid rocks and crust of the earth. The crater of an extinct volcano - its walls coral animals must build on some foun- represented by the corals which have dation. They must begin by attaching grown upon it, its crater represented by themselves to something solid. Every coral reef, therefore, whatever be its form - every line of barrier reef however long -every ring however small or however wide, must indicate some corresponding arrangement of subjacent rock. What cause can have arranged the rocky foundations of the coral in such curious
the harbor in which our ship is lying? The vegetation is not difficult to account for. The coral grows until it reaches the surface. It is known to flourish best in foaming breakers. These, although confronted and in the main resisted by the wondrous tubes and cells, are able here and there in violent storms to break off
the weaker or overhanging portions of the | of coral which build up reefs, so far from coral and dash them in fragments upon the wanting the shelter of a lagoon, are unable top of the reef. Often the waves are to live within it. They can only live and loaded with battering-rams in the shape thrive fronting the open ocean, and in the of immense quantities of drift timber. highly aerated foam of its resisted billows. These bring with them innumerable seeds Moreover, on this view, many species of and hard nuts able to retain their vitality distinct genera and families are supposed whilst traversing leagues of ocean. Such instinctively to combine for one end; and seeds again find lodgment among the of such a combination Darwin declares broken corals, and among the decaying "not a single instance can be found in the pumice. Under tropical heat and moisture, they soon spring to life. The moment a palm-tree rears its fronds, it is visited by birds—especially by fruit-eating pigeons bringing with them other seeds, which are deposited with convenient guano. These in turn take root and live. Each new accession to the incipient forest attracts more and more numerous winged messengers from interminable archipelagoes until the result is attained which so excites our admiration and our wonder, in the atoll islands of the Pacific. All this is simple. But here as elsewhere it is the first step that costs. Are all atolls nothing more than the cup-like rings of volcanic vents? And if they are, can a like explanation be given for the barrier reefs which lie off continental coasts, and where the crater-like lagoon of an atoll is represented only by a vast linear expanse of included and protected sea?
whole of nature." This is rather a sweeping assertion. In the sense in which Darwin meant it, and in the case to which he applied it, the assertion is probably, if not certainly, true. The weapon of analysis, however, if employed upon it, would limit and curtail it much. We cannot indeed suppose that any of the lower animals, even those much higher than the coral-builders, have any consciousness of the ends or purposes which they or their work subserve in the great plan of nature. But Darwin has himself shown us, in later years, how all their toil is co-operant to ends, and how not only different species and families, but creatures belonging to different kingdoms, work together most directly, however unconsciously, to results on which their common life and propagation absolutely depend. In the case before us, however, this second objection of Darwin is superfluous. The first was in itself conclusive. If the reef-building corals cannot live in a lagoon, or in a protected sea, it is needless to argue further against a theory which credits them with working on a plan to insure not their own life and well-being, but their own destruction.
Here were problems eminently attractive to such a mind as that of Darwin. Vast in the regions they affect, complicated in the results which are presented, most beautiful and most valuable to man in the products which are concerned, the facts do nevertheless suggest some physical cause which would be simple if only it But next, Darwin had to encounter the could be discovered. All his faculties theory that atoll islands were built upon were set to work. Analysis must begin extinct volcanoes, and represented nothevery work of reason. Its function is to ing but the walls and craters of these destroy― to pull to pieces. Darwin had well-known structures. This he encounto deal with some theories already formed.tered not with a sweeping assertion, but With some of these he had no difficulty. with a sweeping survey of the vast Pacific. "The earlier voyagers fancied that the coral-building animals instinctively built up these great circles to afford themselves protection in the inner parts." To this Darwin's answer was complete. So far is this explanation from being true, that it is founded on an assumption which is the reverse of the truth. These massive kinds
Had those who believed in this theory ever considered how vast that island-bearing ocean was, and how enormous its supposed craters must have been? It was all very well to apply some known cause to effects comparable in magnitude to its effects elsewhere. The smaller atolls might possibly represent volcanic
craters. But what of the larger? And commanded a wide space of sea, looked what of the grouping? Could any vol- down upon an atoll with its curious ring canic region of the terrestrial globe show of walled-in water, calm, green, and gleamsuch and so many craters as could corre-ing in the middle of the oceanic depths of spond at all to the coral islands? One | blue. Did it not look as if there had once group of them occupies an irregular square been an island in the middle? Did it not five hundred miles long by two hundred look as if the coral ring had been built and forty broad. Another group is eight up upon the rocky foundation of its former hundred and forty miles in one direction, shores? Did it not look as if, somehow, and four hundred and twenty miles in this island had been removed, and the another. Between these two groups there encircling reef had been left alone? Someare other smaller groups, making a linear how! This could not satisfy Darwin. space of more than four thousand miles of How could such an island be removed? ocean in which not a single island rises Its once fringing and encircling reef would above the level of true atolls- that is to have protected it from the devouring sea. say, the level up to which the surf can Did it not look as if it had simply sunk? break and heap up the coral masses, and Subsidence! Was not this the whole to which the winds can drift the result- secret? The idea took firm hold upon ing sands. Some atolls seem to have his mind. The more he thought of it, the been again partially submerged "half- more closely it seemed to fit into all the drowned atolls " as they were called by facts. The coral fringing reef of the Captain Moresby. One of these is of island would not subside along with its enormous size-ninety nautical miles supporting rocks, if that subsidence took along one axis, and seventy miles along place slowly, because the coral animals another. No such volcanic craters or would build their wall upwards as fast as mountains exist anywhere else in our their original foundation was sinking world. We should have to go to the air-downwards. And was there not a perfect less and waterless moon, with its vast vents and cinder-heaps, to meet with any thing to be compared either in size or in distribution. And then, the linear barrier reefs lying off continental coasts and the coasts of the great islands are essentially the same in character as the encircling reefs round the smaller islands. They cannot possibly represent the walls of craters, nor can the long and broad sheltered seas inside them represent by any possibility the cup-like hollows of volcanic
These theories being disposed of, the work of synthesis began in Darwin's mind. He sorted and arranged all the facts, such as he knew them to be in some cases, such as he assumed them to be in other cases. Above all, like "stout Cortez and his men," from their peak in Darien, "he stared at the Pacific." The actual seeing of any great natural phenomenon is often fruitful. It may not be true in a literal sense that, as Wordsworth tells us, "Nature never did betray the heart that loved her." But it is true that sometimes she discloses her secrets to an earnest and inquiring gaze. Sometimes things actually are what they look to be. Outwardly they are what their image on the retina directly paints them; and in their history and causes they may be what that image suggests not less directly to the intellect and the imagination. So Darwin, one day, standing on a mountain from which he
series of islands in every stage of the suggested operation? There were islands with coral reefs still attached to their original foundations, islands with fringing reefs adhering to them all round, and leav ing no lagoons. There were others where the foundations had sunk a little, but not very much, leaving only shallow and narrow spaces of lagoon water between the island and the barrier reef. Others there were again where the same process had gone further, and wide and deep lagoons had been established between the reef and the subsiding island. Then there was every variety and degree of the results which must follow from such a process, until we come to the last stage of all, when the island had wholly sunk, and nothing remained but the surviving reef
a true atoll-with its simple ring of coral and its central pool of protected water. Then further it could not but occur to Darwin that the objection which was fatal to the volcano theory was no difficulty in the way of his new conception; on the contrary, it was in strict accordance with that conception. The vast linear reefs lying off straight and continental coasts, which could not possibly represent volcanoes, were completely explained by a vast area of subsiding lands. The reefs were linear because the shores on which they had begun to grow had been linear also. The immense areas of sheltered sea, from twenty to seventy miles in
breadth, which often lie between the barrier reefs and the existing shores, for example, of Australia and New Guinea, were explained by the comparatively shallow contours of land which had gradually subsided and had left these great spaces between the original fringing reef and the existing shores. The more Darwin pondered, the more satisfied he became that he had found the clue. The cardinal facts were carefully collated and compared. First there was the fact that the reefbuilding corals could not live at any greater depth than from twenty to thirty fathoms. Secondly there was the fact that they cannot live in water charged with sediment, or in any water protected from the free currents, the free winds, and the dashing waves of the open and uncontaminated sea that vast covering of water which in the southern hemi
sphere is world-wide and world-embracing; Thirdly there was the fact that the coral reefs rise suddenly like a wall out of oceanic depths, soundings of a thousand fathoms and more being constantly found close up to the barrier reefs. Fourthly there is the fact that on the inner side, next the island or the continent which they enclose or protect, the lagoon or the sheltered area is often very deep close to the reef, not indeed affording oceanic soundings, but nevertheless soundings of twenty to thirty fathoms. All these facts are indisputably true. Taking them together, the conclusions or inferences to which they point may well seem inevitable. Let us hear how Darwin himself puts them in the short summary of his theory which is given in the latest edition of his journal: —
From the fact of the reef-building corals not living at great depths, it is absolutely certain that throughout these vast areas, wherever there is now an atoll, a foundation must have originally existed within a depth of from twenty to thirty fathoms from the surface. It is improbable in the highest degree that broad, lofty, isolated, steep-sided banks of sediment, arranged in groups and lines hundreds of leagues in length, could have been deposited in the central and profoundest parts of the Pacific and Indian Oceans, at an immense distance from any continent, and where the water is perfectly limpid. It is equally improbable that the elevatory forces should have uplifted throughout the above vast areas innumerable great rocky banks within twenty to thirty fathoms, or one hundred and twenty to one hundred and eighty feet, of the surface of the sea, and not one single point above that level; for where on the whole face of the globe can we find a single chain of mountains,
even a few hundred miles in length, with their many summits rising within a few feet of a given level, and not one pinnacle above it? If then the foundations, whence the atollbuilding corals sprang, were not formed of sediment, and if they were not lifted up to the required level, they must of necessity have subsided into it; and this at once solves the difficulty. For as mountain after mountain, and island after island, slowly sank beneath the water, fresh bases would be successively afforded for the growth of the corals. So certain was Darwin of these conclusions that he adds, in a most unwonted tone of confidence:
other manner how it is possible that numerous I venture to defy any one to explain in any islands should be distributed throughout vast areas all the islands being low, all being built of corals, absolutely requiring a foundation within a limited depth from the surface.*
autumn of 1836, and Darwin landed in The voyage of the Beagle ended in the England on the 2nd of October. He proceeded to put into shape his views on the coral islands of the Pacific, and in May, lic in a paper read before the Geological 1837, they were communicated to the pubSociety of London. His theory took the scientific world by storm. It was well calculated so to do. There was an attractive grandeur in the conception of some great continent sinking slowly, slowly,
into the vast bed of the southern ocean, having all its hills and pinnacles gradually covered by coral reefs as in succession they sank down to the proper depth, until basis of atolls, and these remained, like at last only its pinnacles remained as the buoys upon a wreck, only to mark where some mountain peak had been finally submerged. Besides the grandeur and simplicity of this conception, it fitted well into the Lyellian doctrine of the "bit by bit" operation of all geological causes a doctrine which had then already begun to establish its later wide popularity. Lyell had published the first edition of his famous "Principles " in January, 1830
that is to say, almost two years before the Beagle sailed. He had adopted the volcanic theory of the origin of the coral islands; and it is remarkable that he had nevertheless suggested the idea, although in a wholly different connection, that the Pacific presented in all probability an area of subsidence. Darwin most probably had this suggestion in his mind when he used it and adopted it for an argument which its author had never entertained.†
However this may be, it must have prepared the greatest living teacher of geology to adopt the new explanation which turned his own hint to such wonderful account. And adopt it he did, accordingly. The theory of the young naturalist was hailed with acclamation. It was a magnificent generalization. It was soon almost universally accepted with admiration and delight. It passed into all popular treatises, and ever since for the space of nearly half a century it has maintained its unquestioned place as one of the great triumphs of reasoning and research. Although its illustrious author has since eclipsed this earliest performance by theories and generalizations still more attractive and much further reaching, I have heard eminent men declare that, if he had done nothing else, his solution of the great problem of the coral islands of the Pacific would have sufficed to place him on the unsubmergeable peaks of science, crowned with an immortal name.
the obviously inclining balance has been looked at askance many times. But despite all averted looks I apprehend that it has settled to its place forever, and Darwin's theory of the coral islands must be relegated to the category of those many hypotheses which have indeed helped science for a time by promoting and provoking further investigation, but which in themselves have now finally "kicked the beam."
But this great lesson will be poorly learnt unless we read and study it in detail. What was the flaw in Darwin's reasoning, apparently so close and cogent? Was it in the facts, or was it in the inferences? His facts in the main were right; only it has been found that they fitted into another explanation better than into his. It was true that the corals could only grow in a shallow sea, not deeper than from twenty to thirty fathoms. It was true that they needed some foundation provided for them at the required And now comes the great lesson. After depth. It was true that this foundation an interval of more than five-and-thirty must be in the pure and open sea, with its years the voyage of the Beagle has been limpid water, its free currents, and its followed by the voyage of the Challenger, dashing waves. It was true that they could furnished with all the newest appliances not flourish or live in lagoons or in chanof science, and manned by a scientific nels, however wide, if they were secluded staff more than competent to turn them and protected from oceanic waves. to the best account. And what is one error, apparently a small one, crept into of the many results which have been Darwin's array of facts. The basis or added to our knowledge of nature to foundation on which corals can grow, if it our estimate of the true character and his- satisfied other conditions, need not be tory of the globe we live on? It is that solid rock. It might be deep-sea deposits Darwin's theory is a dream. It is not if these were raised or elevated near only unsound, but it is in many respects enough the surface. Darwin did not know directly the reverse of truth. With all his this, for it is one of his assumptions that conscientiousness, with all his caution, coral "cannot adhere to a loose bottom." * with all his powers of observation, Dar- The Challenger observations show that win in this matter fell into errors as pro- thousands of deep-sea corals and of other found as the abysses of the Pacific. All lime-secreting animals flourish on deepthe acclamations with which it was re-sea deposits at depths much greater than ceived were as the shouts of an ignorant mob. It is well to know that the plebiscites of science may be as dangerous and as hollow as those of politics. The overthrow of Darwin's speculation is only beginning to be known. It has been whispered for some time. The cherished dogma has been dropping very slowly out of sight. Can it be possible that Darwin was wrong? Must we indeed give up all that we have been accepting and teaching for more than a generation? Reluctantly, almost sulkily, and with a grudging silence as far as public discussion is concerned, the ugly possibility has been contemplated as too disagreeable to be much talked about. The evidence, old and new, has been weighed and weighed again, and |
those at which true reef-building species are found. The dead remains of these deeper-living animals, as well as the dead shells of pelagic species that fall from the surface waters, build up submarine elevations towards the sea-level. Again, the reef-building coral will grow upon its own débris-rising, as men, morally and spir itually, are said by the poet to do," stepping-stones of their dead selves to higher things." This small error told for much; for if coral could grow on deep-sea deposits when lifted up, and if it could also grow seaward, when once established, upon its own dead and sunken masses, then submarine elevations and not submarine
* Journal, ed. 1852, p. 477.