visiting many of them, and examining also coralreefs that fringe islands and continents, he offered a theory which for simplicity and grandeur strikes every reader with astonishment. It is pleasant after the lapse of many years to recall the delight with which one first read the Coral Reefs, how one watched the facts being marshalled into their places, nothing being ignored or passed lightly over, and how step by step one was led up to the grand conclusion of wide oceanic subsidence. No more admirable example of scientific method was ever given to the world, and even if he had written nothing else, this treatise alone would have placed Darwin in the very front of investigators of nature.

The second part was entitled Geological Observations on the Volcanic Islands visited during the Voyage of H.M.S. Beagle, together with some Brief Notices on the Geology of Australia and the Cape of Good Hope (1844). Full of detailed observations, this work still remains the best authority on the general geological structure of most of the regions it describes. At the time it was written, the "Crater of Elevation theory," though opposed by Constant, Prevost, Scrope, and Lyell, was generally accepted,

at least on the Continent. Darwin, however, could not receive it as a valid explanation of the facts, and though he did not adopt the views of its chief opponents, but ventured to propose a hypothesis of his own, the observations impartially made and described by him in this volume must be regarded as having contributed towards the final solution of the question.

The third and concluding part bore the title of Geological Observations on South America (1846). In this work the author embodied all the materials collected by him for the illustration of South American geology save some which had already been published elsewhere. One of the most important features of the book was the evidence which it brought forward to prove the slow, interrupted elevation of the South American Continent during a recent geological period. On the western sea-board he showed that beds of marine shells could be traced more or less continuously for a distance of upwards of 2,000 miles, that the elevation had been unequal, reaching in some places at least to as much as 1,300 feet, that in one instance, at a height of 85 feet above the sea,

undoubted traces of the presence of man occurred in a raised beach, and hence that the land had there risen 85 feet since Indian man had inhabited Peru. These proofs of recent elevation may have influenced him in the conclusion which he drew as to the marine origin of the great. elevated plains of Chili. But at that time there was a general tendency among British geologists to detect evidence of sea-action everywhere, and to ignore or minimise the action of running water and wind-drift upon the land. An important chapter of the volume, devoted to a discussion of the phenomena of cleavage and foliation, is well known to every student of the literature of metamorphism.

The official records of the Beagle did not, however, include all that Darwin wrote on the geology of the voyage. He contributed to the Transactions of the Geological Society (vol. v. 1840) a paper on the connection of volcanic phenomena. In the same publication (vi. 1842) appears another, on the erratic boulders of South America; while a third, on the geology of the Falkland Islands, was published later.

He

While dealing with the subterranean agents in geological change, he kept at the same time an ever watchful eye upon the superficial operations by which the surface of the globe is modified. is one of the earliest writers to recognise the magnitude of the denudation to which even recent geological accumulations have been subjected. One of the most impressive lessons to be learnt from his account of Volcanic Islands is the prodigious extent to which they have been denuded. As just stated, he was disposed to attribute more of this work to the action of the sea than most geologists would now admit; but he lived himself to modify his original views, and on this subject his latest utterances are quite abreast of the time. It is interesting to note that one of his early geological papers was on the Formation of Mould (1840), and that after the lapse of forty years he returned to this subject, devoting to it the last of his volumes. In the first sketch we see the patient observation and shrewdness of inference so eminently characteristic of the writer, and in the finished work the same faculties enriched with the experience of a long and busy life. In bringing to light the

operations of the earthworm, he called the attention. of geologists to an agency, the real efficiency of which they probably do not yet appreciate. Élie de Beaumont looked upon the layer of grasscovered soil as a permanent datum-line from which the denudation of exposed surfaces might be measured. But, as Darwin showed, the constant transference of soil from beneath to the surface, and the consequent exposure of the materials so transferred wind, or to be washed to lower levels by rain, must tend slowly but certainly to lower the level even of undisturbed grass-covered land.

be dried and blown away by

To another of his early papers reference may be made, from its interest in the history of British geology. Buckland, following in the footsteps of Agassiz, had initiated that prodigious amount of literature which has now been devoted to the records of the Glacial period in this country, by reading to the Geological Society a paper "On Diluvio-glacial Phenomena in Snowdonia and in adjacent parts of North Wales" (1841). Darwin, whose wanderings in South America had led him to study the problems presented by erratic blocks