CH. V GLACIAL EROSION OF LAKE BASINS. 95 



and thickness of the old glaciers and ice-sheets, and the 

 work they did in distributing huge erratics many hundred 

 miles from their sources and in covering thousands of 

 square miles of country with thick layers of boulder-clay 

 and drift, are all admitted as beyond dispute, geologists 

 are still divided into two hostile camps when the origin of 

 lake-basins is concerned ; and the opposing forces seem to 

 be approximately equal. Having for many years given 

 much attention to this problem, which has had for me a 

 kind of fascination, I am convinced that the evidence in 

 favour of glaciation has not been set forth in all its 

 cumulative force, while many of the arguments against it 

 seem to me to be either illogical or beside the point at 

 issue. I have also to adduce certain considerations which 

 have hitherto been overlooked, but which appear to me to 

 afford very strong, if not conclusive evidence for erosion 

 as against any alternative theory yet proposed. I shall, 

 therefore, first set forth, as fully as the space at my com- 

 mand will allow, the general evidence in favour of the ice- 

 origin of certain classes of lakes, and the special conditions 

 requisite for the production of lakes by this agency. The 

 objections of the best authorities will then be considered 

 and replied to, and the extreme difficulties of the alter- 

 native theories will be pointed out. I shall then describe 

 certain peculiarities, hitherto unnoticed, which clearly 

 point to erosion, as opposed to any form of subsidence or 

 upheaval, in the formation of the lakes in question. Lastly, 

 the special case of the Lake of Geneva will be discussed, 

 as affording a battle-ground that will be admitted to be 

 highly favourable to the anti-glacialists, since most of 

 them have adduced it as being entirely beyond the powers 

 of the ancient glaciers to have produced. 



1. The different kinds of Lakes and their distrihntion. — 

 To clear the ground at the outset, it may be well to state 

 that the great plateau lakes of various parts of the world 

 have no doubt been formed by some kind of earth move- 

 ments occurring subsequent to the upheaval and partial 

 denudation of the country. It is universally admitted 

 that existing lakes cannot be very ancient, geologically 

 speaking, since they would inevitably be filled up by the 



