Reviews — Prof. Bonney — Ice- Work, Present and Past. 229 



are rounded, smoothed, and striated ; and perched blocks and 

 scattered debris indicate that the bulk and sides of a glacier reached 

 to these heights. V-shaped valleys, cut and hollowed out by water, 

 have thus been filled with ice, now gone, leaving smooth and often 

 bare surfaces ; and their moraines, consisting of rocks other than 

 those of the neighbourhood, tell of their former existence and work. 

 The moraines, however, and the generally turbid stream issuing 

 from below the end of the glacier, represent really the talus from 

 the frost-bitten mountain-sides, and relatively but little material 

 removed from the floor or sides of the glacier. The destructive 

 work of mountain-torrents, though spasmodic, is found to be much 

 more important than that of glaciers (p. 22). Thus, it is found (1) 

 that in glaciers of moderate size, such as those of the Alps, the 

 "ground-moraine" is absolutely small; (2) that the ice may abrade, 

 but cannot excavate ; (3) that its movements resemble those of an 

 imperfect fluid. 



The external and internal differences between recent and old 

 moraines are noted ; those near Lake Zurich being examples that 

 the ancient and great glaciers of the Alps advanced and retreated, 

 probably more than once, during the prevalence of an extensive ice- 

 sheet, which reached down over almost the whole of the Swiss 

 low-land, and rose up against the Jura for 3000 feet above 

 Neuchatel lake, and extended northwards to near Soleure. This is 

 indicated on a sketch-map of the glacial movements in France, 

 Switzerland, and part of Germany. The ancient Rhone Glacier had 

 an estimated length of at least 245 miles. 



The glaciers on the southern side of the Alps are the dwindled 

 representatives of gigantic predecessors, which, scarcely less 

 extensive than those on the northern side, descended in the old 

 valleys, passed over the sites of the Italian lakes, on to the plains of 

 Piedmont and Lombardy, as shown by their moraines. 



Land-ice has left its marks on the Alpine region, but in Greenland 

 it is still in possession, representing a Glacial Period there. Records 

 of the temperature and precipitation in Greenland, its configuration, 

 ice-field, and glaciers, are then dealt with. Having collected the 

 evidences of ice-action and its results in Switzerland and Greenland, 

 Dr. Bonney proceeds to a still wider view of glacial phenomena. 



With regard to Arctic and Antarctic ice-sheets, the facts collected 

 by explorers, and summarized by the author, give him such a 

 general idea of the conditions prevailing, and the processes at work 

 during a Glacial Epoch, as follows : — (1) There must have been 

 a mean annual temperature not exceeding 32° F. (2) A fair 

 amount of precipitation, chiefly as snow. (3) An expanse of hilly 

 upland ; huge rolling fells being more favourable than lofty peaks 

 and deep valleys ; the latter would be a region of gigantic glaciers, 

 becoming confluent outside the hill-region. (4) A general gradual 

 slope, for the extension of the ice. (5) Proximity of the 6ea, 

 although favouring precipitation, would restrict the advance of the ice. 



There is heavier precipitation on the Antarctic coasts, and steeper 

 and more uniform surface-slopes; hence their valley -glaciers are far 



