Lakes. 437 



one, though specially looking out for them in many 

 regions, and I believe that they have been only as- 

 sumed by persons who have not realised the meaning 

 of denudations on a large scale, and therefore are apt 

 to consider hills and valleys as the result, mainly, of 

 disturbance and dislocation. From repeated examination, 

 I feel indeed assured, that the Swiss and other valleys 

 generally, and the lake-valleys in particular, do not lie 

 in gaping rents, fissures, or in synclinal curves ; and, 

 indeed, after half a life spent in mapping rocks, I 

 believe that there is no necessary connection between 

 fractures and the formation of valleys, excepting that 

 in certain cases a line of close fracture was also a line 

 of weakness, on which the watery agents that promote 

 denudation were more easily able to work, especially, if 

 on each side of the fault the rocks happen to be of 

 different degrees of hardness. 



It might, however, be said that these lakes lie in 

 areas of special depression, made by the sinking of 

 the land underneath each lake. So difficult indeed did 

 it seem to Playfair, the great illustrator of Hutton, to 

 account for the origin of the rock-basin in which the 

 Lake of Geneva lies, that he was forced to propound 

 the hypothesis that beds of salt had been dissolved 

 underneath its bottom, which therefore sunk, and so 

 formed a hollow for the reception of its waters. Lakes 

 are, however, so numerous in the Alps, North Wales, 

 Cumberland, and the Highlands of Scotland, where they 

 occur by the hundred, and in part of North America by 

 the thousand, that I feel sure the theory of a particular 

 depression for each lake, will not hold in these or in any 

 other northern or southern region that has been acted 

 on by glacier-ice on a great scale. In that part of 

 North America which lies well east of the Rocky Moun- 



