502 THE ICE AGE IN NOBTH AMERICA. 



ing the Ice age, for earlier subsidence during any period of 

 much length, geologically speaking, would have caused the 

 submerged valley to be filled with sediments. The preglacial 

 elevation of the Saguenay region therefore appears to have been 

 at least 1,000 feet greater than now; and it seems to be similarly 

 proved by fiords that nearly the entire extent of the conti- 

 nental glaciated area was considerably higher before than after 

 glaciation. 



There is also evidence that part of the Atlantic coast of the 

 United States close south of the limits of glaciation was at least 

 for a short time preceding the Glacial period uplifted much 

 above its present height. The submarine Hudson River fiord * 

 indicates that the vicinity of New York and Philadelphia then 

 stood 2,800 feet above the sea, and that it afterward slowly 

 sank 1,600 feet, while a bar of that height was formed by coast- 

 wise wash across the mouth of the fiord. In this remarkable 

 preglacial elevation, and in its being more or less shared by the 

 whole northern half of the continent, the formation of the 

 North American ice-sheet seems to be explained. If this was 

 the cause of glaciation, probably the formerly greater height of 

 about 1,000 feet on the Saguenay was not exceptional. In- 

 deed, the elevation there and over large portions of the vast 

 territory of Canada, bounded on the east, north, and west by 

 fiord-indented coasts, may have been much more than is 

 measured by the depth of the Saguenay River. 



Going a step further back, we may regard this northward 

 elevation as a distortion of the earth's form in the storage of 

 energy of lateral pressure which culminated, with the introduc- 

 tion of the new factor of northward depression by the ice 

 weight, in the Quaternary uplifts of the Western plains, the 

 Rocky Mountains, the Sierra Nevada, and the Great Basin. 

 These important changes in the elevations of great areas during 

 the comparatively short Quaternary period seem to be consistent 

 only with the hypothesis that our globe has a comparatively 

 thin crust and a molten interior. 



In the Glacial period significant changes of the sea-level 



* A. Lindenkohl, " American Journal of Science," III, vol. xxix, pp. 475-480, 

 with plate, June, 1885. 



