66 



A NATURALIST IN THE GREAT LAKES REGION 



moraine territory of southern Wisconsin about Gary, for instance; 

 still it is very evidently moraine topography (Fig. 44). 



The melting front of the glacier was pouring out torrents of 

 water that discharged in a mighty river down a valley occupied 

 now by the Desplaines, then the old preglacial valley and much 

 deeper than the present one. The river discharged for a time, 

 at least, into a lake that occupied the Morris Basin (see map), 

 and this in turn had its outlet along the present Illinois Valley 

 then also much deeper. This great river laid down material 

 along its course, for it came away from the glacier so charged 



Fig. 44. — Typical moraine country, kettle-shaped hills and valleys, the 

 latter often with ponds o lakes with no outlet. 



with sediment that wherever its current was checked in the least 

 it deposited the gravel and sand. So it filled up its valley, and 

 tributary streams filled up theirs with long-drawn-out deposits 

 known as valley trains. It spread out a great fan-shaped delta 

 at its entrance into the lake of the Morris Basin. The old valley 

 was filled to a level some fifty feet above the present stream as is 

 evident from the remnants of the old valley train still recogniz- 

 able. *' Opposite Lockport where the road to Plainfield leaves 

 the valley floor" is a flat- topped gravelly ridge, a part of the 

 old valley fill. Some four miles below Joliet there are flat-topped 

 areas of gravel standing up conspicuously in the present valley. 



