CHAPTER XIII
Interglacial Controversies
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, Brückner, 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 palæolithic 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 interglacial 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 Brückner 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 Brückner, 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.