30 Revieics — Br. James Geikie's Great Ice Age. 



and discussed in its pages, and how divergent are the explanations 

 given of the commonest phenomena. There still exist amongst us 

 those who are able to combat skilfully with the pen in favour of 

 such primitive views as the formation of Boulder-clay by cataclysmal 

 deluges of water ; who deny the capacity of glaciers to erode ; and 

 who advocate a portentously rapid elevation of mountain-ranges 

 or the equally sudden submergence of large tracts of country to 

 account for the destruction of one or two species of Mammalia. 

 Views and opinions of this character are treated with scant notice 

 by the author, and not deemed worthy of serious discussion, for he 

 considers that they would long ago have been discarded by those 

 pioneers in this branch of science who originally proposed them. 

 The majority of present-day geologists will be likely to agree with 

 the author in this matter, and they can afford to look with quiet 

 indifference on the resurrection of these old-world views of a past 

 generation. 



A compai'ison of the present book with the edition of 1874 will 

 give a very fair idea of the advances made, and the course and 

 tendency of opinion on Glacial geology since this date. The 

 author assures us that the general position remains the same, and 

 that the additional evidence obtained confirms the view that there 

 was an alternation of cold and genial conditions during the Glacial 

 period, and that Man then lived in Europe. Following the lines 

 laid down in the eai'lier edition, the character and succession of the 

 glacial deposits in Scotland are first described at considerable length, 

 and full particulars are given of the nature and origin of the Till or 

 Boulder-clay, and of the striations and groovings on the rocks beneath 

 it. Then, in a succession of chapters, the stratified and often fossil- 

 iferous beds subjacent to and intercalated with the Boulder-clays 

 are considered, together with those beds which in many places 

 overlie the Till. The question of rock-basins is next taken up, 

 and then the probable formation of district ice-sheets and local 

 glaciers, the relative position of the Arctic shell-beds, and the late 

 Glacial and post-Glacial deposits of that country. Touching on 

 glacial action in connection with the formation of the Boulder- 

 clay, the author thinks that anyone now-a-days who has given the 

 matter sufficient consideration must come to the conclusion that it is 

 of glacial origin. Eespecting the motion of glaciers, the theory of 

 J. D. Forbes that it is due to the quasi-viscous or plastic nature 

 of ice which moves down a slope by its own weight, is accepted as 

 now established by the physical researches of late years, and on this 

 point the experiments of M. Tresca are quoted, which show that the 

 movements of ice under pressure do not fundamentally differ from 

 those of any other solid under similar conditions, and that a mass 

 of it a few hundred feet in thickness, with its temperature at or near 

 the melting point, would, even if it rested on a horizontal plane, 

 flow outwards in all directions until the shearing force came to 

 counterbalance the pressure. 



Summarising the evidence of the glacial and interglacial deposits 

 of Scotland, the author gives a very striking picture of the geological 



