330 



HISTORICAL GEOLOGY 



Two striking features regarding the distribution of the ice were 

 (1) the failure of the ice to cover any of Alaska except its high 

 southern mountain region, though that country is much farther 

 north than most of the glaciated area; and (2) the failure of any- 



Fig. 209 

 Map showing the areas occupied by ice in North America at the 

 time of maximum glaciation. The three great centres of dispersal 

 are indicated. (After Salisbury, from Norton's "Elements of Geol- 

 ogy," by permission of Ginn and Company, Publishers.) 



thing like continuous ice sheets over the high plateaus of the west- 

 ern United States, while the great ice sheet spread over much of the 

 low plains area of the upper Mississippi Basin. 



From its centre of accumulation, the Labradorean ice sheet 

 extended fully 1600 miles southwestward or to about the mouth 

 of the Ohio River. The Kewatin sheet extended from its centre 



