502 



Geological Society. 



examined them in great detail, and left few of their phenomena 

 uninvestigated. Hugi also, in his account of the Alps, and Scoresby, 

 in his descriptions of the arctic regions, have communicated much 

 valuable information respecting glaciers, but without giving rise 

 to any important geological results ; and it was Venetz and De 

 Charpentier who first ascribed to them the transport of the erratic 

 boulders of Switzerland, supposing that the Alps formerly attained 

 a greater altitude than at present, and that the glaciers extended to 

 the plains of Switzerland, and even to the Jura. This assumed 

 greater height of the Alps M. Agassiz dissents from, as no geolo- 

 gical phenomena compel him to admit it ; and the arrangement of 

 the boulders proves that the blocks were not pushed forward by the 

 glaciers, as conjectured by M. Charpentier. Moreover, the phe- 

 nomena of erratic boulders extend over all the temperate and north- 

 ern regions of Europe, Asia and America, and, consequently, could 

 not depend upon so local an event as a greater altitude of the Alps. 

 The consideration of these difficulties induced M. Agassiz to resume 

 the study of glaciers ; and after devoting the suitable portion of five 

 successive summers to the study of their details, and all that has 

 been written respecting their structure, he has arrived at the con- 

 viction, that the formation of glaciers did not only depend upon the 

 actual configuration of the earth, but was also connected with the 

 last great geological changes in the surface of the globe, and with 

 the extension of the great mammifers still found in the polar ice. 

 He has also convinced himself the glaciers did not advance from the 

 Alps into the plains, but gradually withdrew towards the mountains 

 from the plains which they once covered. In this belief, he says, 

 he is supported by many considerations which escaped previous ob- 

 servers, depending chiefly on the form and relative position of the 

 erratic blocks, and the commonly called diluvial gravel, the former 

 being in Switzerland always angular, and resting on the latter, 

 which consists of rounded materials. Considered in this point of 

 view, glaciers assume an entirely new importance, for they introduce 

 a long period of intense cold between the present epoch and that 

 during which the animals existed, whose remains are buried in the 

 usually called diluvial detritus. 



Having established his theory as completely as he could, by re- 

 peated investigations of Switzerland and the adjacent portions of 

 France and Germany, M. Agassiz became desirous of examining a 

 country in which glaciers no longer exist, but in which traces of 

 them might be found. This opportunity he has recently enjoyed, 

 by examining a considerable part of Scotland, the north of England, 

 and the north, centre, west and south-west of Ireland ; and he has 

 arrived at the conclusion, that great masses of ice, and subsequently 

 glaciers, existed in these portions of the United Kingdom at a period 

 immediately preceding the present condition of the globe, founding 

 his belief upon the characters of the superficial gravels and erratic 

 blocks, and on the polished and striated appearance of the rocks in 

 silu. 



M. Agassiz does not suppose that his views respecting glaciers 



