THE GLACIAL PERIOD 



67 



generous remnants of the old valley train. The formation is 

 known as ^'Flathead" (Fig. 45). At a level corresponding to its 

 top on the north side of the valley may be seen a conspicuous 

 shelf of similar gravel along which the upper road runs for some 

 distance. These gravel deposits are rapidly being removed for 

 commercial purposes. 



Small streams rushing from points at the front of the glacier, 

 charged with sediment, often deposited such material close to the 



Fig. 45. — Flathead near Joliet. Detail at right, to show size of the gravel 



glacier's edge as the current was checked when the stream spread 

 out on to the open plain. Such mounds of debris, always irregu- 

 larly stratified, are known as kames. Good examples of such are to 

 be seen one and one-half miles northeast of Naperville, where the 

 road to Wheaton passes between two dome-shaped hillocks, both 

 kames. There is a large one east of Glen Ellyn, cut by the 

 Aurora, Elgin and Chicago Electric Railroad. The east branch 

 of the DuPage River is turned out of its southerly course by it. 

 In the southern portion of the glacier the warm sun melted 

 the ice on its top as ice and snow melt in the early days of spring. 



