438 Lakes. 



tains, and north of latitude 40, it is as if the whole 

 country were sown broadcast with lakes, large and 

 small ; and great part of the country not being moun- 

 tainous, but consisting of undulating flats, it becomes 

 an absurdity to suppose that, so close together, a special 

 area of depression was provided for each lake. The 

 physical geology of America, Scotland, and Sweden, for 

 example, entirely goes against such a supposition ; and 

 I believe that it is equally untenable for the Alps and 

 the lowlands between the Alps and the Jura. Having 

 come to these conclusions, it is plain that it is not a 

 simple thing to account for the existence of hollows, 

 composed of hard rocks, which completely enclose lakes. 



If, then, we have disposed of these erroneous hypo- 

 theses, what is left ? If the sea cannot form such 

 hollows, nor weather, nor running water, and if the 

 hollows were not formed by synclinal curves of the 

 strata, and if they do not lie in gaping fissures, nor, for 

 most lakes, in areas of special depression, the only re- 

 maining agent that I know is the denuding power of 

 ice. 1 



In the region of the Alps it is a remarkable circum- 



1 I must again guard myself against misapprehension. Some 

 lakes owe their existence merely to inequalities in ' the drift ' or 

 other glacial deposits, many to extinct volcanic craters, and others, 

 especially in volcanic regions old and new, to special subsidences. 

 An excellent paper on this subject ' On the Ancient Volcanoes of the 

 District of Schemnitz Hungary,' has been published by Mr. J. W. 

 Judd, F.K.S. in vol. xxxii. of the ' Journal of the Geological Society,' 

 1876 ; and I have no reason to doubt that the Great Salt Lake, the 

 Yellowstone Lake, and others in the barely extinct region of the 

 Eocky Mountains, have a similar origin. Neither would I think of 

 attributing the origin of the great lakes of Africa to glacial 

 influences, any more than I would the Black Sea, the Caspian, and 

 the Sea of Aral. He would also be worse than a bold man, who 

 would speak of the Salt Lakes of the Sahara as being of glacial 

 origin, to say nothing of others too numerous to name. 



