196 



scars are left as evidence of their contact and the force which 

 acted upon them. When the temperature becomes warmer or 

 when the glacier reaches a place of warmer temperature, the 

 ice may melt, thus leaving the rock and sand that were carried 

 (fig. 96). The melting ice forms streams which, as they flow 

 from the glacier, carry away some of the solid material. 





Fn;. 90. The end of a glacier 



The ice is covered with stones and gravel. In the foreground is an accumulation 



of the material which has been brought down by the glacier. Photograph by 



Dr. G. E. Nichols 



Much of North America (fig. 97) was once covered by 

 glaciers, and we still have many evidences of the tremendous 

 effect they have had upon the surface and upon the soil forma- 

 tion. Much of the richest soil of the central United States 

 was brought to its present position by glaciers. A study of 

 the maps of Illinois, Iowa, etc. will show that the so-called 

 corn belt is of glacial origin. 



