Gradually also the difficult task of correlating the interglacial deposits of Britain, Switzerland, and France was being mastered, and even the interglacial periods of North America were being relegated with more or less confidence to their proper places with reference to the European sequence, so that in this, his last book, he was able to announce that solid progress had been made along the lines of advance which he had sketched, and his laborious investigations had produced valuable results. Prof. Geikie had always considered that much valuable knowledge of the climatic changes which Scotland had undergone since the melting of the great ice-sheet would be obtained from a minute examination of the peat-bogs which cover large expanses both of the hills and of the plains of his native country. His own botanical training was insufficient to enable him to attack such a problem with success, but for many years he closely studied the geology of the peat-bogs, and never failed to impress on his students that a rich harvest of scientific information might be reaped by any investigator who took this difficult task in hand. Fortunately he lived to see a very careful examination of the flora of the Scottish peat-bogs by Prof. Lewis published in four parts in _The Transactions of the Royal Society of Edinburgh_. Prof. Lewis was evidently much indebted to Prof. Geikie and to Dr Horne for suggestions and assistance in the geological part of his work; but the evidence, which is very carefully and fully stated in his papers, is sufficient to carry conviction on several important points. He shows that many of the peat mosses began their growth under arctic conditions when glaciers must have existed in many of the more elevated districts of Britain. Thereafter changes of climate supervened, and were accompanied by changes in the flora, of which the remains are now preserved in successive layers of peat. Speaking generally, we may say that the lowest arctic plant bed is followed by a lower forest bed, usually rich in birch (and sometimes hazel and alder), which is overlain by a second arctic bed, followed in turn by a second or upper forest bed containing mostly roots and stools of pine. Above these lies the modern peat. Prof. Lewis concluded as the result of his researches that while it is difficult to reconcile the several stages in the peat with the theory of a single glaciation, the whole of the peat beds agree very closely with the scheme of classification proposed by Prof. Geikie (in the third edition of _The Great Ice Age_ published thirteen years before). These results were none the less gratifying because they had been in some measure foreseen; and if we admit, as some maintain, that the final test of scientific hypothesis is the power to foresee the outcome of future researches, we must agree that Prof. Geikie had good reason to feel that his speculations on late-glacial changes in climate in Britain had not been mistaken.