1882.] 57 [Davis. 



there not other causes besides the five named. Another incon- 

 clusive argument may be noticed here ; it consists in carrying a 

 cause to an extreme in order to disprove it ; for example, if the 

 Swiss lakes are the results of local downfolding or subsidence, 

 how about the numerous small lakes of northern countries? 

 Manifestly we cannot suppose as many subsidences as lakes, for 

 they would be required by the thousand in North America ; 

 hence the Swiss lakes were not produced in this way 1 — a com- 

 plete non-sequitur. It is a little surprising to find this argument 

 elsewhere figuring against glacial action, thus : to admit that our 

 Great Lakes were cut out by erosion, would require us to sup- 

 pose that great enclosed seas, like Hudson's Bay and the Mediter- 

 ranean, and even the ocean itself, were formed in the same way ; 

 but this is clearly impossible ; hence the Great Lakes are not of 

 erosive origin. 2 



We have already shown that there is much to favor the con- 

 structional origin of the Swiss Lakes, and that many of them 

 depend as largely on barriers as on excavation : a similar expla- 

 nation applies to our Great Lakes. The glacial origin of fjords 

 and cirques is advocated chiefly on account of the difficulty of 

 accounting for them in any other way, and not because it is 

 directly shown that glaciers have a great erosive power, or because 

 it is proved that orographic and ordinary erosive forces cannot 

 produce them; they naturally are found in glaciated regions, 

 because both belong in mountainous or rugged districts, and I 

 cannot doubt that further study of the methods of general con- 

 struction and denudation will show us how to account for them. 

 Great glacial erosion thus appears as unnecessary as it is impos- 

 sible, and the argument from necessity becomes inconclusive. 



The author hoped to present in this article an abstract of the 

 line of argument used by each observer quoted in attaining his 

 conclusions ; this has been done in certain cases, and implied in 

 nearly all; but the full carrying out of the plan would have made 

 the paper too long, and it has perforce been modified. The con- 

 clusions are of course in every case no more exact than the ob- 

 servations on which they rest ; and as further study may modify 

 the understanding of certain problems, the resulting conclusions 



1 See Ramsay, loc. cit. 191. 2 Whitney, Climatic Changes, 16. 



