65° 



HISTORICAL GEOLOGY 



Characteristics of Former Drift Sheets. — It will not be advisable to 

 discuss these glacial stages in detail (see references). The different 

 stages varied in duration, in the character of the material deposited, 



Fig. 567. — Map showing the moraines and the direction of the ice movement 

 (shown by arrows) of the last continental ice sheet. The lobate character of the mo- 

 raines is very pronounced. The "driftless area" was not covered by the ice. (Modi- 

 fied after Taylor.) 



and in the extent of the glaciation. The deposits of the Kansan 

 ice sheet, for example, contain little stratified drift, indicating that 

 stream action was of little importance. This is surprising, since the 

 melting of great masses of ice naturally carries with it the idea of 

 flooded streams and great deposits of stratified drift, such as resulted 



