Page:Popular Science Monthly Volume 36.djvu/134

124 Mr. Atkinson and Prof. Mattieu Williams are working in this field, and that their results are received with interest, gives promise that the human race will some time attain to a thoroughly intelligent style of daily life.



formation of coral reefs was one of the subjects investigated by Darwin during the voyage of the Beagle. The information which he obtained from his own observations and the reports of other investigators, together with the mode of accounting for these structures resulting from his study of this material, are embodied in the present work. The first edition of the book was published in 1842, a brief sketch of the author's views having been read in 1837 before the Geological Society, of London, and published. Darwin's theory of coral reefs speedily won acceptance among men of science, and had been taught in scientific lectures and text-books for a generation before any considerable rival appeared. In 1874 Darwin issued a revision of his book, containing additional facts obtained by later explorers. The only important work on the subject which had appeared since 1842 was Prof. James D. Dana's "Corals and Coral Reefs," issued in 1872. Prof. Dana had accepted Darwin's theory in the main, though objecting very decidedly to some of its minor features. In 1880 Mr. John Murray, one of the naturalists of the Challenger Expedition, advanced a theory widely at variance with that of Darwin, which has found vigorous supporters, and various modifications of both the leading hypotheses have been offered by later investigators. But the majority of those qualified to judge of this difficult question have shown a disinclination to give up Darwin's theory for that of Murray—so much so that the Duke of Argyll, evidently jealous for Scottish honor, in 1887 accused scientific men of disregarding Murray's work from subserviency to their idolized Darwin. The duke's article was entitled "A Conspiracy of Silence," and drew forth a vigorous reply from Prof. Huxley in the review in which it appeared, besides arousing a spirited discussion in the columns of "Nature." The new edition of "Coral Reefs" affords the means of forming an intelligent opinion as to the merits of Darwin's views. It is, by the way, the first edition that has been published in this country. The body of the work has been left as revised by the author for the second edition, but occasional foot-notes, and an appendix comprising a careful summary of the more important memoirs published since 1874, have been added by Prof. T. G. Bonney. In the first three chapters the three chief classes of coral formations—atolls or lagoon islands, barrier reefs, and fringing or shore reefs—are described. The fourth chapter deals with the distribution of coral reefs and conditions favorable to their increase, their rate of growth, and the depths at which reef-building corals can live. Darwin's theory of the formation of the different classes of coral reefs then follows. Coral polyps do not flourish below a depth of twenty or thirty fathoms, but reefs are found rising from much greater depths—how are these to be accounted for? The theory regards barrier reefs and atolls as having been developed successively from fringing reefs. The latter are so named because they closely skirt the shores of islands and continental land, increasing by growth on the outer edge, where the conditions seem to be most favorable for the life of the corals. Imagine such a reef formed around a volcanic island, and the island then to begin sinking beneath the sea. The reef will be carried down with it, but the active growth at the outer edge will still keep this part at the sea-level, while the inshore part where growth has stopped will become deeply submerged. We now have an island surrounded by a deep channel, outside of which is a ring of coral—that is, an island encircled by a barrier reef. Suppose the subsidence to go still further until the highest point of the island disappears, the growth at the outer edge of the reef still keeping it up to the surface, and there results a ring-shaped reef inclosing a lagoon—that is, an atoll. It can not be denied that this theory accounts for the channel within a barrier reef and the ring shape of atolls, besides answering the question asked above, 