202 THE ICE AGE IN NORTH AMERICA. 



Hitchcock,* require the ice of the Glacial period to be eight 

 miles deep over the central part of Labrador ; and, if the 

 movement came from Greenland, the same slope of forty- 

 five feet to the mile would reach, at that point, the astonish- 

 ing depth of eighteen miles. 



It is not necessary, however, to suppose a uniform slope 

 to the center of so vast an ice field. If, however, we assume 

 with Chamberlin and Salisbury, f that there was an actual 

 movement of glacial ice of 1,600 miles from the Labradorian 

 center to the southern part of Illinois, and of equal extent 

 from the Keewatin center west of Hudson's Bay to Topeka, 

 Kansas, an average slope of but ten feet to the mile would give 

 a depth of three miles at the centers. That the depth was as 

 great as this, seems the more probable from the fact that the 

 Keewatin center is low, and unless the elevation of that 

 region was then much greater than it is now the movement 

 must have been produced by the pressure caused by the simple 

 accumulation of ice. Staggering to the imagination as these 

 suppositions are, they seem to be inevitable inferences from 

 the established facts. A depth of three miles over the central 

 portions of the glaciated area in North America is, therefore, 

 by no means improbable. 



* "New Hampshire Geological Report," vol. iii, pp. 320, 321. 

 t Geology, vol. iii, pp. 330, 357. 



