The first edition of The Great Ice Age was completed in manuscript in 1873, and in the previous year James Geikie had already published a series of papers in the Geological Magazine which clearly outlined his main conclusions. All the essential features which were to distinguish his life-work in this highly controversial field are already recognisable in these papers. The principal characteristic of The Great Ice Age is its literary ability, the power of lucidly expounding intricate scientific theories and sketching the evidence on which they rest in a manner which equally avoids prolixity and obscurity. Although, as we have shown, he was by no means the first to champion the cause of land ice as against floating ice as the dominant factor in the production of the drift, he was immediately accorded the place of protagonist in this cause. In Scotland his views, at any rate among his colleagues on the Survey, were those generally accepted. In England also the Survey geologists were in agreement with him on most of the essential points, though the submergence hypothesis and the efficiency of floating icebergs were long held in esteem in the sister kingdom, and have not yet completely fallen into disrepute. In Germany, Norway, Sweden, Holland, and in North America there had as yet been no general enlightenment on the real merits of this controversy. It may be noted that in the first edition of his Great Ice Age, James Geikie did not deny the fact that a great submergence accompanied the main glaciation of Britain. He accepted it indeed, though in later years he saw reason to modify this opinion.

The efficiency of land ice to explain most of the puzzling features of the drifts was the main thesis which the book was written to uphold. But there were many subordinate problems which came up for consideration. One of these is the amount of erosion which the ice-sheets and glaciers had produced. In this James Geikie followed very closely in the footsteps of Ramsay ; on the origin of rock-basins, fjords, and sea lochs there is in fact practically complete agreement in their views. This is the more significant, because Ramsay was at that time far ahead of educated geological opinion on these matters, and it is only quite recently that his views have received acceptance in some of the most influential geological circles.

Another burning question which fell to be considered was the evidence for or against interglacial warm periods; a question which even at the present time is almost as keenly debated as it was in 1874 when The Great Ice Age was published. As years went past and successive editions of the book appeared, the battle of land ice versus floating ice may be said to have been definitely closed; and James Geikie's name as an expounder of glacial geology came to be more and more closely associated with his views on the glacial succession (the question, that is, whether there was only one epoch of glaciation, or several epochs separated by periods in which the climate was much milder). On this subject, as on glacial erosion, James Geikie took up his position very strongly from the first and maintained it to the end.

In considering this branch of James Geikie's scientific work we may trace a considerable amount of influence exerted on his thought by James Croll, one of the most remarkable geologists that Scotland has produced. Croll was a man who started life in a very humble position; he educated himself, and by sheer power of intellect and dogged perseverance he attained eminence in scientific work. He was at once a metaphysician and a physicist, but it is only with the latter aspect of his teaching that we are here concerned. Though quite unschooled in mathematics he was daunted by no difficulties, and by laborious calculation he worked out intricate problems of astronomy ; and the accuracy of his solutions was afterwards confirmed by professional mathematicians and astronomers. Croll saw at a very early stage that to land ice must be ascribed practically the whole of the glacial phenomena of Scotland. He inferred from a number of facts that the North Sea had been filled with Scandinavian ice during the maximum stages of glaciation, and he suggested lines of research to James Geikie, John Home, and Benjamin Peach that led to important contributions to the literature of Scottish glacial geology. Crol pondered long and deeply over the causes of the Ice Age and the origin of changes of climate in general, and the result was a series of papers in which he maintained that changes in the eccentricity of the earth's orbit and the obliquity of the ecliptic, accompanied by other astronomical processes, might produce epochs of cold climate in one hemisphere with warmer conditions in the opposite hemisphere. These changes might under certain conditions be sufficient to account for the existence of ice-sheets. During the later years of his life Croll was a member of the staff of the Geological Survey of Scotland, and this silent, reserved, studious man was widely recognised as a most original thinker.

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.

The post-glacial history of Scotland was a subject that early attracted James Geikie's attention. He had devoted much study to it, and was in after years to present a masterly analysis of its stages and sequence. To trace the connection between the Ice Age and the present day, and to show the changes which had elapsed since the ice-sheets melted from the surface of Britain, was to him one of the most alluring departments of geology. A good deal of work had been done by Scottish geologists on the study of the raised beaches of Scotland, but no general account of their relation to one another and to the glacial boulder-clay and moraines had appeared before the publication of the first edition of The Great Ice Age. That the sea-level had undergone alterations around our shores was sufficiently demonstrated by the raised beaches, of which three were very well known, the 100-foot, 50-foot, and 25-foot beaches.

But some authors, such as Chambers and Mackintosh, were ready to find raised beaches anywhere; gravel terraces at all elevations, many of which are now known to have been the deposits of glacial rivers and lakes, and rock escarpments and platforms of very varied origin, were appealed to as evidence of former submergence beneath the sea. Prof. Geikie at this stage was not altogether free from a belief in the great submergence, or at any rate he was not prepared to challenge its champions ; but he knew how little value was to be attached to some of the evidence cited in its support, and his own studies had led him to a fuller understanding and a more satisfactory appreciation of the meaning of the raised beaches and the light they threw on the varied conditions that had prevailed in Scotland during and subsequent to the melting of the great ice-sheet. In particular, he maintained that the higher beaches were associated with the deposits of clay containing glacial shells that were so well known through the researches of Smith of Jordanhill, and belonged to a time when glacial conditions had not completely ceased in Scotland. The 50-foot beach was associated with the oldest relics of man in the midland valley of Scotland, while the 25-foot beach and lower beaches were laid down in climatic surroundings differing little from those of the present day. Between the epochs of depression which these sea-terraces recorded there had been intervals when the land stood at a higher level, so that the earth movements had been of an oscillating character, and not merely a succession of uplifts with intervening pauses during which the beach-platforms were produced. The buried forests and the peatbogs furnished additional evidence of the elevation and depression of the land, and hinted, not obscurely, at the probability that changes of climate had also taken place during post-glacial time, the warm continental epochs encouraging the growth of trees, while the cold, damp, insular climates were favourable to the accumulation of peat. Although these conclusions were only sketched out and not fully stated, it is plain to the reader that already Prof. Geikie had convinced himself of the importance of these facts.

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 palaeolithic 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 Home'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 palaeolithic 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 Durnten 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 inter-glacial 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 minutiae 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 palaeolithic 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 ioo-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.