THE QUATERNARY PERIOD 331 



southward nearly as far, or into northern Missouri. These two 

 great ice sheets practically merged. "One of the most marvelous 

 features of the ice dispersion was the great extension of the Kewatin 

 sheet from a low flat centre westward and southwestward over what 

 is now a semiarid plain, rising in the direction in which the ice 

 moved, while the mountain glaciers on the west, where now known, 

 pushed eastward but little beyond the foothills" (Chamberlin 

 and Salisbury). 



The Cordilleran ice sheet appears to have been mostly made 

 up of both plateau and typical mountain (Alpine) glaciers. To- 

 ward the south it extended only a little way over the high moun- 

 tains of the northwestern United States. 



Newfoundland, and possibly also Nova Scotia, had local centres 

 of glaciation. 



South of the ice sheets above described, the higher mountains 

 of the United States, even as far south as southern California, 

 Arizona, and New Mexico, bore numerous glaciers greatly varying 

 in size. These were always of the typical valley or Alpine types 

 instead of ice sheets. Some of these mountains, such as Shasta, 

 Hood, Rainier, and those of the Glacier National Park in Montana, 

 still have glaciers, the greatest being those of Mount Rainier, where 

 they attain lengths of from 4 to 6 miles. 



Direction of Movement and Depth of Ice 



The fact that glacial ice flows as though it were a viscous sub- 

 stance is well known from studies of present-day glaciers in the 

 Alps, Alaska, and Greenland. A common assumption, either that 

 the land at the centre of accumulation must have been thousands 

 of feet higher, or that the ice must have been immensely thick, in 

 order to prevent flowage so far out from the centre, is not necessary. 

 For instance, if one proceeds to pour viscous tar slowly in one place 

 upon a perfectly smooth (level) surface, the substance will gradu- 

 ally flow out in all directions, and at no time will the tar at the 

 centre of accumulation be very much thicker than at other places. 

 The movement of the ice from each of the great centres was much 

 like this, only in the case of the glacier the piling up of snow and 

 ice was by no means confined to the centres of accumulation. 



Some of the finest examples of the influence of topography 

 upon the direction of movement of the ice are afforded by New 



