108 



ISLAND LIFE. 



[part 1. 



head of the Lake of Geneva, since it spread over the whole of 

 the great valley of Switzerland, extending from Geneva to 

 ISTeufchatel, Berne, and Soleure, and even on the flanks of the 

 Jura, reached a maximnm height of 2,015 feet above the valley. 

 The numerous blocks scattered over the Jura for a distance of 

 about a hundred miles vary considerably in the material of 

 which they are composed, but they are found to be each trace- 

 able to a part of the Alps corresponding to their position, on 

 the theory that they have been brought by a glacier spreading 

 out from the Rhone valley. Thus, all the blocks situated to the 

 east of a central point G (see map) can be traced to the eastern 

 side of the Rhone valley (/ e d), while those found towards 

 Geneva have all come from the west side h). It is also very 

 suggestive that the highest blocks on the Jura at G have come 

 from the eastern shoulder of Mont Blanc in the direct line 

 /i. B F G. Here the glacier would naturally preserve its 

 greatest thickness, while as it spread out eastward and westward 

 it would become thinner. We accordingly find that the 

 travelled blocks on either side of the central point become lower 

 and lower, till near Soleure and Geneva they are not more than 

 500 feet above the valley. The evidence is altogether so con- 

 clusive that, after personal examination of the district in com- 

 pany with eminent Swiss geologists. Sir Charles Lyell gave up 

 the view he had first adopted — that the blocks 'had been car- 

 ried by ice during a period of submergence — as altogether 

 untenable.^ 



The phenomena now described demonstrate a change of 

 climate sufficient to cover all our higher mountains with 

 perpetual snow, and fill the adjacent valleys with huge glaciers 

 at least as extensive as those now found in Switzerland. But 

 there are other phenomena, best developed in the northern part 

 of our islands, which show that even this state of things was 

 but the concluding phase of the glacial period, which, during 

 its maximum development, must have reduced the northern 

 half of our island to a condition only to be paralleled now in 

 Greenland and the Antarctic regions. As few persons besides 

 professed geologists are acquainted with the weight of evidence 

 1 Anfiquity of Man, 4th Ed. pp. 340-348. 



