The subject-matter was now, of course, so vastly enlarged that only the more important contributions could be adequately noticed, and much interesting detail had to be passed over or handled only in the briefest way. Many of the old controversies which had bulked largely in the first and second editions of the book had been decided, or had been so fully discussed that there was no pressing need to devote much space to them; but the subject as a whole was not less involved in uncertainty and debate, for new topics of discussion had arisen, hardly less keenly disputed than the old ones. In the main lines of his argument Prof. Geikie still followed the teaching of Ramsay and Croll and the geologists of the old Scottish school, and though, for example, no longer inculcating the necessity of a great glacial subsidence, he maintained most of the positions he had taken up in his early days. In one respect, however, the work marked a great advance, for he now believed it possible to subdivide the history of _The Great Ice Age_ into a succession of glacial and interglacial periods with far more minute detail than he had hitherto attempted. In this he showed a boldness which some critics might call rash, but which has been in very large measure justified by the results of subsequent research. He came to be recognised as pre-eminently the defender of interglacial periods; and to this aspect of the book far more attention has been directed than to any other. James Geikie, in fact, was soon considered an ultra-interglacialist, if we may coin a ponderous but perhaps expressive term. The technical details of the evidence cannot be discussed in this place; it will be sufficient to say that he believed there was good evidence in Scotland and in Europe generally for the former existence of no less than six glacial periods separated by intervals of milder climate which were truly interglacial.