The second edition of The Great Ice Age was sold out about the year 1892, and the author set himself to the task of preparing a third edition, incorporating all the most recent investigations. The task was necessarily a very severe one, as an enormous increase had taken place in the number of workers in this field, and the evidence had accumulated at a very rapid rate. Prof. Geikie always regarded this work as his principal contribution to geological literature, an opinion which most of his critics seem to have shared ; and certainly the labour he spent on the third edition of his magnum opus was sufficient to entitle it to a high place in the history of glacial investigation. With indomitable perseverance he undertook the work of mastering the literature, and the number of papers he read may be inferred from the fact that his collection of pleistocene and glacial pamphlets, which now form a part of the noble library of the University of Edinburgh, numbered over one hundred and sixty volumes. He aimed at making the book not only a compendium of information on the subject of which it treated, but also a critical review of the conclusions which might fairly be drawn from the evidence to hand; and in this he not unfrequently differed from the authors of the papers he cited, a proceeding which was likely to awaken feelings the reverse of grateful.

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.

At the time the book was published it is no exaggeration to say that he was alone in holding these views. Glacial investigation had made considerable progress in Scotland since 1877, when the second edition of his book was issued; but most Scottish geologists, though in agreement with Prof. Geikie on many points, would hardly have followed him in the extreme position which he took up. That interglacial periods had existed they generally admitted, but the searching criticism to which the evidence in favour of them had been subjected had revealed that much of it was of an indecisive character, if not actually untrustworthy; and no British geologists of that time had Prof. Geikie's wide knowledge of the glacial literature of other countries. They were consequently often unable to appreciate how far the continental evidence filled up the gaps which were painfully evident in the record of British glacial history. In certain circles, in England especially, the evidence for interglacial periods was regarded with sceptical distrust, if not completely disbelieved; but on Clement Reid, his former colleague on the Survey, and one of the most skilled and critical glacialists then living, it had produced a different impression. He saw clearly the necessity for admitting the existence of at least one interglacial period; but between his position and that of James Geikie, who believed in five interglacial periods, a great gulf intervened. Perfectly aware of his apparent isolation, and supremely confident in the accuracy of his results, James Geikie pressed strongly on his readers the necessity of appreciating more fully the significance of the facts, and in consequence his book became very obviously an argument in favour of Pleistocene and Recent oscillations of climate rather than a critical and impartial review of the evidence available. In every case he went as far in support of his conclusions as the facts in his opinion could be interpreted to lead; and the treatment of British glacial questions showed undoubtedly a stubborn courage and a determination to make the best of his case, which only his confidence in the general sufficiency of the evidence for the whole of Europe could be held to justify.

In foreign countries generally he found more support, though everywhere, it may be admitted, his views must have been regarded as extreme. In Germany glacial investigation was still in a comparatively backward state, but in Penck, Bruckner, and Partsch (names subsequently to figure most prominently in the story of the advance of this department of science) he found disciples and supporters of the highest value. The investigations of these geologists had led them independently to the belief in the repeated glaciation of the Alps and the mountains of Central and Eastern Europe. Their chief results were still to appear, but enough was known of their conclusions to define their attitude. In Norway and Sweden, though many notable investigations into glacial geology had been made, no general consensus of opinion had been reached as to the stages into which the glacial history of that country must be subdivided, and Prof. Geikie still found his old friend Axel Blytt the nearest in agreement with his views among the Scandinavian geologists. In France the existence of interglacial periods had warm defenders and keen opponents; but attention was being directed more particularly to the successive phases of palaeolithic culture, in the study of which French geologists and anthropologists have always been in the forefront. But in America a school of geologists had arisen in which Prof. James Geikie had found not only warm personal friends but also powerful supporters in his theoretical views, and a most notable contribution to the third edition of The Great Ice Age are the chapters by Prof. Chamberlin (cf. Part I., p. 120), in which the glacial history of North America is reviewed. The literature of the glacial geology of that continent has now swelled to enormous dimensions, and to describe the phenomena in a critical and discriminative manner was beyond the powers of anyone who had not devoted many years to a personal examination of the evidence; but in Prof. Chamberlin an exponent was secured who was not only in very substantial agreement with Prof. Geikie in his conclusions, but was also exceptionally familiar with the facts.

The general reception of Prof. Geikie's book was deferential if not enthusiastic. The masterly handling of the subject was freely admitted, and the thorough and scholarly manner in which the sources of information had been searched; but no symptoms appeared to indicate the existence of a school of advanced interglacialists, in Britain at any rate, prepared to accept and defend the author's theoretical views. In fact, for a time it almost seemed as if the belief in the reality of inter-glacial periods, or at least in their importance, was less prevalent than it had been fifteen years before. A very large body of geologists declined to regard the evidence on which Prof. Geikie and his supporters relied as having real value or significance. There were still a few supporters of the theory of the marine origin of boulder-clay, and even some who were prepared to advocate the agency of floods and debacles as the prime factors in the formation of boulder-clay; and their views for some years were prominent in the discussion of the origin of glacial deposits. The majority of experienced geologists certainly did not accept these explanations; but they were equally unwilling to concede that the Ice Age could be subdivided into six glacial epochs, alternating with warmer climates in which Northern Europe and America had been occupied by a fauna and flora of temperate facies.

Prof. Geikie lived to see very considerable changes in the opinion of geologists on these matters. As time went on much new evidence accumulated to prove that great fluctuations of climate had marked the recent stages of the earth's history. From many sides facts were reported which tended to support his theories. Gradually it came to be recognised that the ice margin must have withdrawn at times for considerable distances, leaving bare wide tracts of country which became populated by animals and plants. Still,, however, it was contended that these were mere episodes of no great account, temporary retreats and advances of the ice-sheets, unworthy to be designated glacial and interglacial periods. But the increase of knowledge renders this position less and less tenable as years go by, and it may fairly be claimed that before Prof. Geikie's death, in most countries of Europe and North America the existence of several interglacial periods was freely conceded by a majority of those who were competent to express an opinion on the subject.

The important new evidence brought to light was not wholly the result of geological investigation, though much of it was strictly of the kind to which Prof. Geikie had appealed. Most striking perhaps were the descriptions of the glacial phenomena of the Alpine valleys which Profs. Penck and Bruckner published in a famous volume in 1909. This work was most appropriately dedicated by the authors to Prof. James Geikie. It is probably the most notable contribution to the literature of glacial geology in the last twenty years, and although it has not escaped criticism, it has produced in the minds of impartial readers a firm conviction of the occurrence of glacial and interglacial periods so far as that part of Europe is concerned. Prof. Geikie was familiar with some of the evidence from the Alpine chain when he was writing the third edition of The Great Ice Age; some of the facts had led geologists to postulate the existence of interglacial periods as long ago as the middle of last century; but he watched with great pleasure the gradual accumulation of observations added to previous knowledge by Penck and Bruckner, and for many years he maintained an active correspondence with these investigators. In America, also, the opinion was gradually gaining strength that the Ice Age was marked by several prolonged intervals of warmer conditions; and in France, Germany, and Scandinavia many geologists were added to the ranks of those who maintained the importance of interglacial periods.

Hardly less convincing than the results of Penck and Bruckner's investigations into the repeated glaciation of the Alps were the advances which have been made by the study of paleolithic deposits, especially in France, Belgium, and Germany, during the last twenty years. In popular interest this chapter of geological history necessarily surpasses all others, and the study of the deposits of the caverns and river valleys which contain the rude stone weapons of early man and the remains of the wild animals which he hunted has never lacked enthusiastic investigators. In particular, the geologists and anthropologists of France have distinguished themselves by their patience and success in this department; and the palaeolithic history of Europe is now far more fully known than it was in 1895. These investigations have shown not only that man inhabited Northern Europe before the cold conditions of the glacial period had passed away, as Prof. Geikie had stoutly maintained from an early period in his career, but also that cold epochs had alternated repeatedly with warmer epochs. Differences of opinion, of course, there are, as is inevitable in subjects which at the present time have been so incompletely examined. Penck and Geikie, for example, would place the epoch of weapons of Acheulian type in the second interglacial warm period, while Boule and Schmidt would relegate it to the third; but the significant fact remains that there is a general agreement that since man inhabited Northern Europe he has seen repeated epochs of genial climate alternating with periods of severe cold.

Prof. Geikie was always deeply interested in this work, and followed the course of investigation with the closest attention. Unfortunately Scotland possesses no deposits containing palaeolithic weapons; and circumstances precluded him from taking part in the field studies except during brief holiday visits to the Continent; but he diligently read the literature, as may be seen in his course of Munro lectures in Edinburgh University in 1913, subsequently published in book form as The Antiquity of Man in Europe. In reading this book, it is pleasant to find how little change he had been obliged to make in the conclusions he had arrived at twenty years before, and how fully his sagacious interpretation of the evidence then available had stood the test of time. One can notice in his preface a serene conviction that his work had been justified by the results.

"The research of the past twenty years has certainly cleared up much that was doubtful and obscure, and brought to light many interesting details which enable us to form a more adequate conception of the early history of our race than was previously possible. These later investigations, however, have not in any respect shaken the general conclusions arrived at twenty years ago but, on the contrary, have served only to strengthen and confirm them."

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 Home 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.

When in course of time the third edition of The Great Ice Age was sold out, he considered very carefully whether he should undertake a revision of the book, bringing it up to date by incorporation of the most recent additions to our knowledge of the glacial period. Advancing years made him to some extent reluctant to undertake so formidable a task, and he felt also that in his interpretation of the chief events of this chapter of geological history he had no radical alterations to make. This, as we have already said, is sufficiently clear from his attitude in his Munro lectures. Moreover, the whole subject was highly controversial, and he greatly disliked fighting the old battles over again. At one time he was seriously thinking of writing a short work outlining the most important recent advances in glacial geology, but the intention was never carried into effect.

Problems of tectonics and of the relations between geological structure and the surface configuration of the earth at the present time always possessed a strong fascination for him, and in his college lectures were favourite topics for discussion. Belonging to both geology and geography, these were subjects in which all his powers found congenial exercise. The Scottish Geographical Magazine contains many papers from his pen dealing with physical geology, and the last of these which he wrote was on "The Deeps of the Pacific Ocean and their Origin." In this paper he, advocated a new interpretation of these great submarine depressions, and as his views were not in accordance with those of Prof. Suess of Vienna, as expounded in his great work The Face of the Earth, this paper was the occasion of a long and friendly correspondence with the eminent Austrian geologist (an Englishman by birth). Prof. Geikie had always been a great admirer of Suess and a close student of his writings, and both were attracted by the same kind of problems. In 1911 Prof. Geikie had written a paper on the "Architecture and Origin of the Alps" which appeared in the Scottish Geographical Magazine, and ten years previously more than o'ne paper on the origin and structure of mountains had been contributed by him to various journals. He now determined to use the materials he had collected for the preparation of a book which was ultimately issued under the title Mountains: their Origin, Growth, and Decay. As usual he did not despise the non-scientific reader, but made his exposition of the subject so simple and clear that all could apprehend his meaning. A vast amount of important work had been done on the geological structure of the Alps during the previous ten years, and in addition to reading the literature carefully, Prof. Geikie visited Switzerland to make himself familiar with the scenes he described, and to enable him to form an opinion on the theories advanced, based on personal examination of some of the best sections. At the same time he utilised the results of the work of his old colleagues of the Scottish Survey on the Northwest Highlands, where they had gleaned new data of the highest value, and the book was illustrated with many beautiful photographs of Scottish and Alpine mountains. Throughout the book the influence of Prof. Suess is often noticeable. The compilation of this book was a thoroughly congenial task to Prof. Geikie. He was content for a time to let glacial controversies rest, and to concentrate his attention on problems of geographical evolution.

In bringing to a close this short review of Prof. Geikie's scientific work, we may be permitted to point out what seems to be the main characteristics of his investigation and teaching. Had he been questioned himself on this point, there can be no doubt he would have given his University courses of instruction a high place in his services to science. He never allowed himself to regard it as routine work, to be hurried through without enthusiasm. He gave his best to his students, and constantly improved his lectures, excursions, and practical classes, so as to make them as modern and as complete as circumstances would allow. Hampered by very inadequate accommodation and equipment, he gave freely of his time and money to compensate for these disadvantages. The ordinary student he strove to interest and to instruct, and as year by year his classes increased, he had good evidence to convince him that both his subject and his method of expounding it were receiving their full share of attention among the students of the University. But he had a keen eye for merit, and young men who evinced a desire to pursue the path of original research were quickly recognised and encouraged in every way to follow the right lines. Thus, although geology was for a long time a very small class, it produced almost every year one or more men who subsequently made a name for themselves in science. All over the world, and especially in the British colonies, there are many well-known geologists who can trace the impetus which decided their careers to the lectures delivered by the genial professor in the dingy old Edinburgh class-room at the top of those interminable stairs.

As a geologist he had limitations which he clearly recognised. Paleontology, petrology, and mineralogy he had a sound working knowledge of, but he never professed to know them thoroughly, and much of the teaching of these subjects he left to specially trained assistants. Had he been better equipped in these respects, he might have avoided some of the pitfalls into which he stumbled at times. But in physical and structural geology he took a very high place among living scientists. The thorough training and natural aptitude for structural and field geology made him a very shrewd judge of controversial questions in tectonics, and laid a secure foundation for his researches in geographical evolution and the origin of the earth's surface features. As a geographer, interested especially in the larger problems of geographical configuration, he earned a world-wide reputation. His special field of work, however, was the history of the glacial period in all its aspects, and as time went on he came to be recognised as the most thorough-going advocate of repeated glacial and interglacial epochs. The positions he took up at a very early stage in his scientific career he maintained with little modification till its close, and in spite of indifference and in the face of severe criticism he saw his theories more and more completely established year by year. The subject is one of the most controversial in geological science at the present day. Very eminent authorities may be found who deny the validity of nearly every one of Prof. Geikie's conclusions about interglacial epochs, but there is a large and increasing body of supporters of his views, though even now the extreme position he took up in subdividing the Ice Age into six glacial periods cannot be said to be generally accepted. But if we compare the textbooks of the present day with those published twenty years ago, we can realise how great an advance has been made in the direction in which he led; and there can be no doubt that in the long-run his consistency, courage, and sagacity will receive full recognition.

The old Scottish school of geology which had numbered so many famous men among its members found in James Geikie one of its most distinguished representatives. In science, as in all things, he was pre-eminently a Scotsman. Ramsay and Croll, two of the most philosophic geologists of their time, were the men to whom he owed the inspiration which originally directed him, and he was a true disciple of Playfair, whose memory he reverenced. In all his writings he places in the foreground the observations which he and his fellow-workers in Scotland had made in the field, and the inferences drawn from them ; and it was in no small measure to James Geikie that the high position which the work of Scottish geologists holds in the estimation of scientific men is to be ascribed.