286 GENERAL SCIENCE 



nent the glaciers of the ice age had considerable to do with 

 the soils of certain sections. As these great fields of 

 ice moved south they carried great quantities of material 

 from the old mountain chains of Southern Canada. 

 This rich material was distributed over the northern 



FIG. 246. Mountain Disintegration in the Alps. 

 The accumulated debris on the right is rock in process of decay. 



part of the United States to be ground finer and redis- 

 tributed with each return of the glacier (Figure 247). 

 Many regions owe the fertility of their soils largely to the 

 work done by the great seas of ice. 



Composition of Soils. - - The wealth of our agricultural 

 communities lies in the fertility of their soils. An agri- 

 cultural soil is made of (a) decayed rock, (6) soil water, 

 (c) soil air, (d) decaying organic matter, (e) living organ- 

 isms. In general we may say that fertile soils have all 

 of the above constituents ; however, drained swamp lands 

 (muck soils) are usually very fertile although deficient 

 in rock particles. 



