198 MAN AND THE GLACIAL PERIOD. 



It seems impossible to account for such a deep gorge 

 extending so far below the sea-level, except ujDon the sup- 

 position of a long-continued continental elevation, which 

 should allow the stream to form' a canon to an extent 

 somewhat comparable with that of the canons of the 

 Colorado and other rivers in the far West. Then, upon 

 the subsidence of the continent to the present level, it 

 would remain partially or wholly submerged, as we find it 

 at the present time. During the Glacial period it was so 

 filled with ice as to prevent silting up. The rivers enter- 

 ing the Pacific Ocean, both in the United States and in 

 British Columbia, are also lost in submerged channels ex- 

 tending out to the deeper waters of the Pacific basin in a 

 manner closely similar to the Atlantic streams which have 

 been mentioned. 



During this continental elevation which preceded, 

 accompanied, and perhaps brought on the Glacial period, 

 erosion must have proceeded with great intensity along 

 all the lines of drainage, and throughout the whole re- 

 gion which is now covered, and to a considerable extent 

 smoothed over, by glacial deposits, and the whole country 

 must have presented a very different appearance from 

 what it does now. 



A pretty definite idea of its preglacial condition can 

 probably be formed by studying the appearance of the 

 regions outside of and adjoining that which was covered 

 by the continental glacier. The contrast between the 

 glaciated and the unglaciated region is striking in several 

 respects aside from the presence and absence of trans- 

 ported rocks and other debris, but in nothing is it greater 

 than in the extent of river erosion which is apparent upon 

 the surface. For example, upon the western flanks of the 

 Alleghanies the regions south of the glacial limit is every- 

 where deeply channeled by streams. Indeed, so long have 

 they evidently been permitted to work in their present 

 channels that, wherever there have been waterfalls, they 



