Feb. 26, 1 8 74 J 



NATURE 



319 



cases, perhaps, as little more than troublesome hindrances 

 to the making of a good geological map. Thus it came 

 about that deposits of this class were lumped together 

 under the comprehensive title of Diluvium or Northern 

 Drift : and that, in the few cases where any geologist 

 thought them worthy of more than a simple recognition, 

 the explanations offered of their origin were crude and 

 unsatisfactory. Some of these explanations we may just 

 glance at. In the days when evolution and continuity 

 were doctrines yet undreamed of, it was imagined that 

 between any two consecutive geological epochs there 

 intervened a period of chaotic turmoil, one result of 

 which was, that a clean sweep was made of the life of the 

 epoch that had just closed, and the ground prepared for 

 the introduction of the life of that which was to follow. 

 Supposing this to have been the general course of past 

 events, some referred diluvial accumulations to the series 

 of convulsions which came in like a great gulf between 

 the age of man and the last of geological eras. It could 

 not be reasonably objected to such an hypothesis that it 

 called to its aid agencies the like of which we had never 

 seen, and the like of which, as far as our knowledge of 

 the economy of nature went, it was most improbable had 

 ever been in operation ; there was the ready answer, that 

 during periods which were essentially abnormal, anything 

 was possible. This made such explanations easy to 

 frame and easy to uphold, and they commended them- 

 selves readily to the indolence of mind and impatience of 

 accurate thought from which few of us are altogether 

 free. The same may be said of the notion suggested by, 

 but we cannot say based upon, the phenomena of the 

 great ocean wave of earthquakes, " that somehow and 

 somewhere in the far north a series of gigantic waves was 

 mysteriously propagated," which " were supposed to have 

 precipitated themselves madly on over mountain and 

 valley alike, carrying along with them a mighty bur- 

 den of rocks, stones, and rubbish," and that by this 

 means the piles of diluvium had been heaped up. Again, 

 the name diluvium was founded on the idea that its 

 deposits were the relics of Noah's flood ; and the notion 

 that we had in them a proof of the accuracy of the Bib- 

 lical record was so very welcome, that it was accepted 

 and stuck to in spite of the absence of evidence in its 

 favour, and so contributed, perhaps as much as anything 

 else, to postpone the true solution of the problem. 



But by degrees light began to dawn on the subject. 

 Playfair had attempted to turn the attention of geologists 

 to the proper quarter, when he suggested that the most 

 powerful agents which Nature employs for the moving of 

 rocks are the glaciers ; but his hint lay for a while un- 

 heeded. In 1837, Agassiz arrived at the conclusion that 

 the glaciers of the Alps had been formerly far larger than 

 at present. He had studied the smoothed and (urrowcd 

 surfaces which occur everywhere below glaciers, and had 

 found that the rocks displayed markings exactly identical 

 with these far beyond the range of the present ice. He 

 explained his views to Buckland, who then saw the mean- 

 ing of certain surface features which he had observed, but 

 had not previously understood, in the British Islands. 

 The two geologists visited Scotland together in 1S40 ; 

 found over the length and breadth of the land scorings 

 and polishings which ice— and, as far as their knowledge 

 went, nothing but ice — could have made, and came to 



the conclusion that the whole country had been once 

 swathed in one widespread ice-covering. About the same 

 time Sir Charles Lyell attributed the formation of portions 

 of the Scotch drift to the action of land-ice. 



The right clue was now found, and it only remained for 

 others to follow it up. A great step was made by Prof. 

 Ramsay when, some ten years later, he deciphered the 

 story written on the Drift-beds of North Wales, and 

 determined the broad succession of physical changes that 

 had led to their formation. He pointed out that there 

 had been two periods of cold, the first of intense severity, 

 and the second less rigorous, and that between the two 

 there came a milder interval, during which depression 

 brought the sea up the flanks of the mountains to a 

 height of 2,300 feet above its present level. 



Still however the importance of the Drift was far from 

 being fully recognised. For many years no notice whatever 

 was taken of it on the maps of the Government Survey ; and 

 when at last it met with a tardy recognition. Drift was 

 still for a while Drift " and it was nothing more," a some- 

 thing agriculturally important and therefore not to be 

 passed over by the economic geologist, but hardly a great 

 formation vi'ith a story to tell as long, as varied, and as 

 interesting, as any that geology had hitherto revealed to 

 us. It is significant that ever so eminent a pioneer as 

 Prof. Ramsay did not deem these deposits worthy of more 

 than incidental notice in his otherwise exhaustive Memoir 

 on the Geology of North Wales. The Drift in fact was 

 somewhat on the position of a nouveau riclie, who is 

 trying to work his way into " society," and it had up-hill 

 work before it was admitted into the exclusive circle of 

 the old respectable formations. 



But its turn came at last, and amid the band of geo- 

 logists, who have helped in the work of securing for it 

 the attention to which it is fairly entitled, the brothers 

 Geikie occupy prominent places. The one gave us in 

 1863 his paper on the phenomena of the Glacial Drift of 

 Scotland, in which he offered a masterly summaiy of all 

 that was known on the subject up to the date of its publi- 

 cation, and settled for ever the claim of land-ice against 

 ice-bergs to have been the agent that formed the Scotch 

 Till ; and now the other comes before us with the goodly 

 volume, whose title stands at the head of this article, and 

 which can be cordially recommended both to the geo- 

 logist and the general reader. Its account of the labours 

 and conclusions of previous workers is all but exhaustive, 

 but it is far more than a mere ii-siDiii j a long practical 

 acquaintance with Drift-deposits has enabled the author to 

 add materially to our knowledge of the course of events 

 that accompanied their formation, and in some cases has 

 led him to demur to views hitherto all but universally 

 accepted ; and his own contributions and criticisms are 

 as remarkable for the boldness of their originality as for 

 the soundness of the reasoning by which they are upheld. 

 At the same time the explanations are so full, and the 

 method of handling so free from technicality, that with a 

 moderate amount of attention the book may be under- 

 stood, and its reasoning followed, by those who had pre- 

 viously little or no geological knowledge. 



A large part of the work is taken up by a careful and 

 detailed description of the Drift-beds of Scotland, which 

 country the author has chosen as a typical area. A 

 better selection could not have been made, for in no 



