V GLACIAL EROSION OF LAKE BASINS 127 



it is shown that both the sub-aqueous contours of the 

 lake-basins, and the superficial outlines pf the lakes, are 

 exactly such as would be produced by ice-erosion, while 

 they could not possibly have been caused by submergence 

 due to any form of earth-movements. It is submitted 

 that Ave have here a positive criterion, now adduced for 

 the first time, Avhich is absolutely fatal to any theory of 

 submersion. 



Lastly, the special case of the Lake of Geneva is dis- 

 cussed, and it is shown that the explanation put forth by 

 the anti-glacialists is wholly unsupported by facts, and is 

 opposed to the known laws of glacier motion. The 

 geologists who support it themselves furnish evidence 

 against their own theory in the ancient alluvium at 

 Geneva on which the glacial deposits rest, and which is 

 admitted to be mainly derived from the distant Alps. But 

 as all alluvial matter is necessarily intercepted by large 

 and deep lakes, the presence of this Alpine alluvium im- 

 mediately beneath the glacial debris at the foot of the 

 lake, indicates that the lake did not exist in pre-glacial 

 times, but that the river Rhone flowed from the Alps to 

 Geneva, carrying with it the old alluvium consisting of 

 mud, sand, and gravel, which it had brought down from 

 the mountains. Still more conclusive, however, is the fact 

 that the three special features which have been shown to 

 indicate erosion rather than submergence are present in 

 this lake as fully as in all other Alpine valley-lakes and 

 unmistakably point to the glacial origin of all of them. 



On the whole, I venture to claim that the facts and con- 

 siderations set forth in this chapter show such a number 

 of distinct lines of evidence, all converging to establish 

 the theory of the ice-erosion of the valley-lakes of highly 

 glaciated regions — a theory first advocated by the late 

 Sir Andrew Ramsay — that that theory must be held to 

 be established, at all events provisionally, as the only one 

 by which the whole body of the facts can be explained 

 and harmonized. 



