570 Reviews — Professor W. H. Hobbs — Existing Glaciers. 



glaciers are moulded with reference to the irregularities of their beds. 

 In the former " no portion of the lithosphere is exposed above its 

 higher levels. The glaciers of mountains, on the contrary, always 

 have rock exposed above their highest levels ". There are, however, 

 small ice-cap or plateau glaciers, as in Norway and Iceland, which to 

 some extent are transitional between the larger ice-sheets and the 

 mountain glaciers, though more closely allied to the former because 

 they rest on a comparatively flat foundation. In the ice-covered 

 archipelago of Franz Josef Land the islands are almost completely 

 snow-capped by neve of low density rather than by compact glacier ice, 

 while the group of islands known as Spitzbergen exhibits inland ice, 

 small ice-caps, and true mountain glaciers. In the references to this 

 region (p. Ill) the name of Professor Garwood should have been 

 mentioned. 



In dealing with mountain glaciers the author commences with 

 a discussion on the origin of cirques, that are so characteristic of 

 mountains which are or have been occupied by glaciers. In explaining 

 their origin he supports the views of Messrs. W. D. Johnson and F. E. 

 Matthes. Snow-banks were formed on shallow depressions of steep 

 slopes, and by a process of 'nivation', due to frost and melting snow, 

 rock-material was broken up and the original depression deepened. 

 Ultimately the snow-banks assumed the functions of glaciers, and 

 removed blocks of rock disintegrated from the walls of the cirques, 

 which in form were at first nearly circular. 



This subject is dealt with in considerable detail and is well 

 illustrated, and it leads on to descriptions with explanations of the 

 higher rock-features of the 'Fretted Upland', where we find various 

 types of ridges, needles, etc. Portion of a hill-shaded map of the 

 country between Bethesda and Llanrwst is reproduced to illustrate 

 a 'karling' or high district dissected by cirques. Some reference is 

 made to the influence of a glacial cover in protecting its base from 

 ordinary weathering processes, but the author is hardly justified in 

 speaking (in his preface) of a school of British geologists "which 

 holds that the denudational effect of glacier ice is negative, because it 

 protects the basement from the process of weathering". Various 

 types of mountain glaciers dependent on the amount of snow supplied, 

 or ' alimentation ', are described and illustrated ; and the excavation 

 of U-shaped and hanging valleys is attributed to the widening and 

 deepening accomplished by the ice through combined abrading and 

 plucking processes. Attention is given to the problems of glacial 

 sculpture in Scandinavia and other high latitudes, to the fjords or 

 deep and now partially submerged U -valleys, that were occupied by 

 glacier streams, the courses of which, initiated by pre-existing fractures, 

 may also have been guided by the work of earlier rivers. 



That " the Pleistocene glaciation consisted of some four distinct 

 glacial cycles which were characterized by relatively mild climatic 

 conditions", is regarded by the author as well recognized, though he 

 should have added, "by some distinguished glacialists." A short 

 account of the glacial features due mainly to deposition concludes 

 Part I. 



In Parts II and III we have descriptions of the more extensive 



