James Geikie was much attached to Croll, and while he never professed to be versed in the mathematical branches of science, he was prepared to accept the accuracy of Croll’s theories. The other causes of glaciation which had been advanced by various geologists, such as Lyell’s hypothesis of elevation and depression of the land, he believed to be quite inadequate, and in the first edition of _The Great Ice Age_ he states Croll’s hypothesis with evident approval, or at any rate regards it as the only explanation at that time offered which could be held to be at all in accordance with the facts. From this position Geikie never receded. In subsequent years Croll’s hypothesis was the subject of strenuous discussion. Eminent astronomers like Sir Robert Ball found in it a satisfactory explanation of Pleistocene glaciation. Equally eminent astronomers like Simon Newcomb after testing it found it wanting. The subject as a whole was beyond the scope of Geikie’s work, which was geological rather than astronomical or meteorological; and in his later years he rather avoided the discussion of the causes of glaciation, but he made it clear that in his opinion, if Croll’s hypothesis failed, no other explanation could be regarded as adequate. As a corollary of Croll’s theory, it followed that there had been more than one period of arctic cold in the northern hemisphere, and that intercalated between the cold periods there were epochs of warmer climate--interglacial periods, as they are now called. The evidence for the existence of interglacial periods had appealed to Geikie in his field work, and he had become convinced that in Scotland there had been at least one interval of mild climatic conditions separating two epochs of glacial severity. This may have to some extent predisposed him to favour Croll’s hypothesis as being in greatest accordance with the geological facts. For it cannot be said that James Geikie was in a hurry to maintain the complexity of the Ice Age. In the first edition of his book, though much engrossed in the description of the beds intercalated with the boulder-clay and “till,” and obviously inclined to attribute great importance to them, he says very little about warm interglacial periods, and the reader is not led to suppose that he considers the evidence as of overwhelming strength. Three years later the second edition of _The Great Ice Age_ appeared, and we find that the author then took up a much more definite position on this subject, and has made a great advance in his treatment of it. But already in 1873 he was convinced in his own mind that several warm interglacial periods had interrupted the rigours of the Ice Age, though he did not attempt to enumerate the interglacial epochs in detail, or to state fully the conclusions at which he had arrived.