No. •!.] DAWSON — POST-PLIOCENE. 409 



the submerged valley of the St. Lawrence. Lastly, the power 

 attributed to glaciers as eroding agents, has been found to be 

 altogether fallacious. I was surprised, in visiting the x\lps in 

 1865, to find that this boasted erosive power was little else than 

 a myth; and I see that since that time many other observers 

 have arrived at similar conclusions. I have recently seen a very 

 sensible view of this question in a popular book by the well- 

 known Alpine explorer, Whymper, of which I may quote the 

 concluding paragraph, as precisely stating my own view as ex- 

 pressed in the Canadian Naturalist in 1866: 



" Tf I were asked whether the action of glaciers upon rocks 

 should be considered as chiefly destructive or conservative, I 

 should answer without hesitation principally as conservative. 

 It is destructive certainly to a limited extent ; but like a mason 

 who dresses a column that is to be afterwards polished, the 

 glacier removes a small portion of the stone on which it works 

 in order that the rest may be more effectually preserved."* 



Some of the ablest of the advocates of the action of continen- 

 tal glaciers have recently in my opinion contributed largely to 

 the overthrow or modification of the theory. I may refer to 

 two examples. 



Prof. Dana has given the coup de grace to the American con- 

 tinental glacier by his paper in the No. of Silliman's American 

 Journal for November, 1871. In this paper he affirms that 

 '' the idea of a central glacier source for the continent is without 

 foundation," so that it comes to be a question of local glaciers. 

 He demands, however, one very large glacier of this kind. South- 

 east striae occur on the mountains of New England to a height of 

 5000 to 5200 feet above the sea. A glacier to make these must, 

 as he admits, have moved from a higher level. But N.W. of these 

 striated mountains lie the valley of Lake Champlain and the 

 great plain of the St. Lawrence, the latter with S. W. striae at 

 right angles to those on the mountains. Still farther in the same 

 direction is the valley of the Ottawa, and between this and the great 

 low region of Hudson's Bay is only the Laureutian watershed 

 of about 1500 feet high. From this must have flowed the glacier 

 which passed over the tops of the White Mountains. In order 

 to effect this result, it is necessary to suppose an elevation of the 

 Hudson's Bay watershed in the Post-pliocene period to at least 



* Whymper, " Scrambles amongst the Alps," 



