106 MAN AND THE GLACIAL PERIOD. 



Valley, where in the vicinity of Fort Wayne an extensive 

 terminal moraine was formed. 



The much-mooted question of a succession of glacial 

 epochs finds the most of its supporting facts in the por- 

 tion of the glaciated area lying west of Pennsylvania. 

 That there have been frequent oscillations of the glacial 

 front over this area is certain. But it is a question 

 whether the glacial deposits south of this distinct line of 

 moraine hills are so different from those to the north of 

 it as to necessitate the supposition of two entirely distinct 

 glacial epochs. This can be considered most profitably 

 here. 



The following are among the points with reference to 

 which the phenomena south of the moraine just deline- 

 ated differ from those north of the line : 



1. The glacial deposits to the south appear to be dis- 

 tributed more uniformly than those to the north. To the 

 north the drift is often accumulated in hills, and is dotted 

 over with kettle-holes, while to the south these are pretty 

 generally absent. Any one travelling upon a line of rail- 

 road which traverses these two portions of the glaciated 

 area as indicated upon our map can easily verify these 

 statements. 



2. The amount of glacial erosion seems to be much 

 less south of the line of moraine hills delineated than 

 north of them. Still, glacial strias are found, almost every- 

 where, close down to the extreme margin of the glaciated 

 area. 



3. The gravel deposits connected with the drainage of 

 the Glacial period are much less abundant south of the 

 so-called " terminal moraine of the second Glacial period " 

 than they are north of it. South of this moraine the 

 water deposits attributed to the Glacial period are of such 

 fine silt as to indicate slow-moving currents over a gentle 

 low slope of the surface. 



4. The glacial deposits to the south are more deeply 



