And in considering what is probably the most controversial problem which the student of Pleistocene and recent times must investigate, namely, the relation of prehistoric man to the glacial period, he followed the same line of thought, considering that the evidence of the mammalian remains found in caves and river gravels of Northern Europe pointed to the conclusion that there had been great variations of climate. The mixture of northern and southern types of animals was not to be ascribed in his opinion to migrations arising from seasonal changes, but was due principally to alternations of cold and heat, each enduring for a considerable time. He advocated also the existence of man in glacial times, and recapitulating views already enumerated in some papers which he had published in the Geological Magazine, he argued that the palæolithic gravels of England were to be regarded as glacial and preglacial, and not, as was widely believed, of interglacial and post-glacial age.
Lastly, we may mention a feature of the first edition of The Great Ice Age that was to become more prominent in subsequent editions, the comparative description of the phenomena described by geologists of many different countries. For information regarding England he was largely indebted to his colleagues in the English Survey, principally Green, Tiddeman, and Whitaker. The Swedish, German, Norwegian, and continental deposits generally had perforce to be described from the literature of the subject, a literature already very extensive. Through his whole life Prof. Geikie was a diligent student of the literature of his subject. The most important European languages, as already noted in [Part I.], he could read with facility, and as he was in constant receipt of copies of glacial papers from their authors, much of his time was taken up with a study of the contemporary literature of glaciation. It was his familiarity with the work of other investigators in this field of scientific research that gave him his position as the representative British glacialist, and made his works so widely read and appreciated by foreign scientific men.
With the publication of the first edition of The Great Ice Age in 1874, Prof. Geikie’s reputation as a glacial geologist of the first rank was at once established. The book had a cordial reception and a ready sale. Prof. Green wrote a long and very sympathetic review of it for Nature, and, whether its teachings were generally accepted or not, the author had the satisfactory proof that it had not been neglected by the rapid exhaustion of the first edition. Within a few months he had to set seriously about the production of a new and enlarged edition. Much of its popularity was no doubt due to the clear and graceful style in which it was written. The more abstruse parts of the subject were not discussed with too much detail; great insistence was placed on the field evidence, and the discussion was such as could be followed by the general reader who had no special training in geological work. A studied moderation marked the conclusions arrived at, and no attempt was made to force a revolutionary interpretation of glacial phenomena into prominence. A great deal also was due to the fact that the book embodied not only its author’s work and the hypotheses he favoured, but also the results of the observations of many of his colleagues on the Survey who had a very wide acquaintance with field geology, and were, on the whole, very well agreed regarding the interpretation of the facts. The author fully acknowledged his obligations to colleagues on the Survey staff, but at the same time it was clear that on this subject he was the leader and not merely a compiler of other people’s results. The dedication to Sir Andrew Ramsay is especially significant, for from Ramsay more than from any other geologist had inspiration been received.
Probably the effect of the book was greater in foreign countries than in Britain. In Germany, Switzerland, Sweden, and the United States many geologists were actively prosecuting the study of glacial deposits, and so clear and authoritative a statement of the observations and conclusions of the Scottish glacialists had much interest to workers in other lands. This appreciation the author valued greatly, and it was the cause of a great enlargement in the circle of his correspondents. He followed keenly the advance of glacial investigation in foreign countries, and especially the new evidence brought forward regarding changes of climate during and subsequent to the glacial period, and the early chapters in the history of man in Europe.
The second edition, which appeared three years after the first, showed that the author had been led to modify his views in several important respects. The great post-glacial submergence he now considered unproved, following in this the conclusions arrived at by Dr Jamieson of Ellon in his studies of the Scottish glacial deposits. He recognised also that the shelly boulder-clay of many parts of Scotland, such as Caithness, Orkney, Shetland, Dumbartonshire, and Ayrshire, was best explained on the lines suggested by Dr James Croll as the deposit of an ice-sheet that had invaded the land after travelling for a time over the sea bottom. In this we see the influence of Dr Peach and Dr Horne’s work on the glaciation of Caithness, Shetland and Orkney, and of Geikie’s own investigation of the glacial phenomena of the Outer Hebrides. These changes of opinion were undoubtedly well considered, and have been supported by subsequent discoveries. He also took up a much bolder attitude on the question of interglacial deposits and the relation of man to the Ice Age. While still relying to the full on the evidence cited from Scotland in the first edition of The Great Ice Age in favour of the existence of more than one interglacial period, he adduced the results of Skertchly’s work at Brandon as proving that the palæolithic deposits of south-eastern England are in places overlain by genuine boulder-clay. More prominence was also given to the continental evidence for interglacial periods, especially to that obtained in the Dürnten lignite of the north side of the Alps, and of the so-called Pliocene beds of Lombardy, which even in the first edition he had confidently claimed as being really interglacial.
The next important work from Prof. Geikie’s pen was Prehistoric Europe, published in 1881. He continued to keep abreast of the rapidly increasing literature of his subject, and although the main lines of his treatment of it required little modification, he was continually adding to his store of facts. Prehistoric Europe did not receive the same welcome as The Great Ice Age, and this could hardly be expected. Geologists were by this time familiar with the author’s main conclusions, and the book in some measure takes us over familiar ground. But to the general reader it remains one of the most enjoyable of the author’s contributions to the literature of science.
Having already expounded in his previous works the essential phenomena of glaciation, he devotes this book especially to the consideration of many questions of subordinate importance, though in themselves deserving of full consideration. The interglacial problem, of course, comes up for treatment, but he has not much to say of it that is really new to his readers. It is interesting to note, however, that less insistence is now laid on the Scottish evidence in favour of interglacial periods, and the British evidence in general, and more is said of the interglacial beds of Germany, France, Italy, Switzerland, and other European countries. The feeling seems to have arisen in the author’s mind that much of the British evidence was not so strong as to carry conviction, and the work of continental geologists was rapidly adding details of the highest significance to the store of accumulated observations in favour of repeated glaciations of Northern Europe. We may readily believe also that he felt it desirable to enforce on the minds of his readers the value of much recent research done by his fellow-scientists in other countries. Many British geologists assumed and still maintain a very sceptical attitude regarding the value of the British evidence for interglacial periods, and Prof. Geikie was undoubtedly right in appealing rather to well-established facts in adjacent countries than attempting to discuss the minutiæ of sections often of a temporary nature and by no means well-exposed, which were familiar to many of his British readers. It is not to be supposed, however, that he had changed his ground; to the last he maintained the validity of the British evidence for interglacial periods, though in some parts of it modifications of his original statements might have become necessary. In the nature of things the evidence collected from so small an area as Scotland was sure to be incomplete, and to treat Great Britain as a region apart was more likely to lead to error than to correct results.
Another subject which he handled more fully than in The Great Ice Age was the antiquity of the human relics of palæolithic type which had been found in caves and river gravels. Many British geologists of the highest reputation held that these were of post-glacial date, but Prof. Geikie had always contended strongly that some at least of the deposits containing the implements of early man were interglacial or preglacial. Time has justified his sagacity, and it is now fairly widely recognised that these relics date back in some cases to periods anterior at any rate to the last glaciation of Northern Europe. The old controversy regarding changes of climate in Pleistocene time reappears in this volume, and the author stoutly maintains the position he had taken up in The Great Ice Age, that the association of the remains of mammals of southern and northern types in gravel deposits can be explained only on the hypothesis that periods of genial alternated with periods of arctic climate.
But perhaps the main purpose of this book, as seems to be indicated by the title selected for it, was to discuss the changes that had taken place in Europe since the melting of the ice of the last stage of the glacial period. The phenomena of the raised beaches that encircle our Scottish coasts, with the alluvial or “carse” clays of the river valleys intimately associated with the beach deposits, and the peat and buried forests of our moorlands and coasts, had fascinated Prof. Geikie since the beginning of his glacial investigations, and he felt that for their proper discussion more scope was required than was afforded by such a book as The Great Ice Age. These problems were full of difficulties and the evidence appeared often contradictory or misleading, but he managed to piece it together and to arrive at a consistent and clearly reasoned interpretation. The raised beaches indicate, of course, changes of the level of sea and land; but these were far more considerable than the beaches alone would indicate, as the submerged forests that in many places are intercalated with the beach and carse deposits show that at certain stages the land area had been far more extensive than at present. This was confirmed by many facts regarding the present distribution of animals and plants in the British Isles which could not otherwise be logically explained; and in this field of investigation he gratefully acknowledges the assistance furnished by his old friend Dr Buchanan White, with whom he was in close contact since he was then living in Perth. The raised beaches also were associated with the closing phases of glaciation in Britain, since both the 100-foot and the 50-foot beaches in the north of Scotland showed effects of contemporaneous glacial action, and the older marine shell beds contained shells now living only in Arctic seas. The interpretation of the evidence to be obtained from the study of peat-bogs and buried forests was by no means so clear, but indubitably pointed towards the recurrence of damp cold epochs suitable for the rapid growth of peat, separated by epochs of a different character during which the country was overspread by a dense growth of forest. These hypotheses had long occupied the author’s mind, and he had pondered deeply over the evidence in support of them. Fuller investigation in future years was destined to bring out many striking confirmations of his opinions. It may be said that so far as his interpretation of the post-glacial history of Scotland is concerned, the most authoritative opinion of Scottish geologists at the present time is in accordance with the conclusions which he had arrived at. This alone makes the book still worth careful study by those who would appreciate the changes our islands have undergone in the most recent stages of their geological history, and though notable additions have been made to the store of accumulated observations, they readily find a place in the scheme which he has outlined.