nishing a delightful narrative to the general reader, and laying the foundation for generalisations of surpassing importance to all thinking minds.

It was evident to many geologists that the greatest value would attach to the full record of the geological observations made by the gifted young secretary of the Geological Society. A year after the publication of the Journal the first portion of these observations, dealing with coral reefs, was almost ready, but the continued illhealth of the author delayed the publication till 1842. When it appeared, under the title of "The Structure and Distribution of Coral Reefs," its success was immediate and complete.

Ever since their first description by voyagers, marvel had been expressed at the strange and beautiful phenomena presented by coral islands. Coral, as being built up by the tireless labours of innumerable so-called "insects," or "worms," had become associated with romantic ideas. It really consists of the internal skeletons of coral-polyps, allied to the sea anemone. Captain Basil Hall, in his "Voyage to Loo Choo," looking with the eyes of one ignorant of zoology, had credited the building of coral reefs to all kinds of creatures which lived on and near the coral after it had been made; and his erroneous views had been amplified and developed by James Montgomery, in his "Pelican Island," into the most fantastically incorrect description that ever versifier penned. Sad to relate, his lines were often quoted, as if correct, by scientific men in pre-Darwinian times.

Nothing gives clearer evidence of the power of mind which Darwin had already attained when voyaging round

the world than the originality of his views on coral reefs. The lagoon islands, or atolls, he describes as "vast rings of coral rock, often many leagues in diameter, here and there surmounted by a low verdant island, with dazzling white shores, bathed on the outside by the foaming breakers of the ocean; and, on the inside, surrounding a calm expanse of water which, from reflection, is of a bright, but pale, green colour." Keeling atoll, outside which, at less than a mile and a half distance, no bottom was found with a line 7,200 feet in length, having been fully described, and an account given of all other known atoll systems, the peculiarities of the great barrier reef of North-east Australia, and that of New Caledonia, were recounted. Off the latter, no bottom was found, at two ships' length from the reef, with a line 900 feet long. With these were linked the smaller reefs of Tahiti and others, where considerable islands are more or less completely surrounded by them. Next, the fringing or shore reefs, at first sight only a variety of barrier reefs, were clearly distinguished from them by the absence of an interior deep-water channel, and their not growing up from an immense, but from a moderate depth of

water.

The remarkable fact was pointed out by Darwin that all coral islands are within a little more than 30 degrees of the Equator, but that, at the same time, they are absent over certain larger areas within the tropical seas. There are none on the West Coast of South America, nor on the West Coast of Africa. In this portion of his work we have another significant sentence bearing on the struggle for existence. In discussing the apparently capricious

distribution of coral reefs, he remarks that "the study of the terrestrial and better-known half of the world must convince every one that no station capable of supporting life is lost-nay more, that there is a struggle for each station between the different orders of nature." He describes the large fishes and the trepangs (holothuria) preying upon the coral-polyps, and shows how complex are the conditions which determine the formation of reefs on any shore. Perhaps no part of his work is more important than that in which he collects the evidence proving how rapidly coral masses grow, and that they for the most part cannot flourish in a greater depth of water than fifteen fathoms.

Reasoning upon the facts observed by himself and others Darwin now proceeded to upset the received theory that atolls were based upon submarine volcanic craters, and to substitute for it the view that there has been a prolonged and gradual subsidence of the areas upon which the atolls are based, and a corresponding upward growth of the reefbuilding corals. Thus fringing-reefs in time become barrier-reefs; and barrier-reefs, when they encircle islands, are converted into atolls, or lagoon islands, as soon as the last pinnacle of land sinks beneath the surface of the ocean. The whole matter is summed up thus: "A magnificent and harmonious picture of the movements which the crust of the earth has within a late period undergone is presented to us. We see vast areas rising, with volcanic matter every now and then bursting forth through the vents or fissures with which they are traversed. We see other wide spaces slowly sinking without any volcanic outbursts; and we may feel sure that this sinking must

have been immense in amount as well as in area, thus to have buried over the broad face of the ocean every one of these mountains above which atolls now stand like monuments, marking the place of their former existence." "No more admirable example of scientific method was ever given to the world," says Professor A. Geikie, "and even if he had written nothing else, this treatise alone would have placed Darwin in the very front of investi gators of nature."

After thirty-two years' interval, a second edition of "Coral Reefs " appeared, in a cheaper form, in 1874. It is rare indeed for a scientific treatise to attain at once and maintain so long a position of such undisputed authority. The eminent German naturalist, Semper, in 1863, criticised the general theory in consequence of his own careful examination of the Pelew Islands; but Darwin easily answered him by pointing to the cumulative evidence in favour of his own views. The only really important work on the subject, after Darwin's, was that of Professor J. D. Dana, the eminent American naturalist and geologist, on "Corals and Coral Islands," published in 1872. Darwin, in the preface to his second edition, candidly acknowledged that he had not previously laid sufficient weight on the mean temperature of the sea in determining the distribution of coral reefs; but this did not touch his main conception. In fact, he maintained his ground undisturbed, and at the same time admired. greatly Dana's book, which was the result of personal examination of more coral formations than perhaps any one man had ever studied, and which accepted Darwin's fundamental proposition, that lagoon islands or atolls

and barrier-reefs have been formed during periods of subsidence.1

No such strikingly original theory is propounded in the second part of "The Geology of the Beagle," dealing chiefly with volcanic islands. St. Jago, in the Cape de Verde Islands; Fernando Noronha, Terceira, Tahiti, Mauritius, St. Paul's, Ascension, St. Helena, and the Galapagos are in turn more or less fully described, according to the opportunities the explorer had possessed. To some extent, as in the succeeding part, Darwin adapts his views on mountain elevation too closely to those enunciated by Elie de Beaumont. The third part of the geology of the Beagle, entitled "Geological Observations on South America," was not published till 1846. Even this did not exhaust the contributions to geology made from the Beagle voyage, for it did not include the papers on the "Connection of certain Volcanic Phenomena in South America" (1838); on the "Distribution of Erratic Boulders" (1841); on the "Fine Dust which falls on

'Mr. John Murray's views, derived from the experience acquired in the voyage of the Challenger, and published in 1880, tend to modify Darwin's conclusions to some extent. Mr. Murray says that it is now shown that many submarine mountains exist, which are usually volcanic, and which, being built upon by various forms of shellbearing animals, could be raised to such a level that ordinary corals could build upon them. He concludes that probably all atolls are seated on submarine volcanoes, and thus it is not necessary to suppose such extensive and long-continued subsidences as Darwin suggested. This view is also in harmony with Dana's views of the great antiquity and permanence of the great ocean basin. See "The Structure and Origin of Reefs and Islands." By John Murray; Proc. Roy. Soc., Edin., x. 505-18 (abstract); also Nature, xxii. 351-5.