68 



PRINCIPLES OF AGRICULTURAL CHEMISTRY 



miles from the base of the mountains, the deposits being in places 

 five hundred feet thick. These deposits are now being eroded 

 and reworked by streams. 



Fig. 17. Profile showing how a river builds up its banks 

 near the channel. U. S. D. A. 



Alluvial soils, especially if deposited by large rivers, are derived 

 from a mixture of minerals from different sources. The soils 

 are more or less generalized and are usually very productive. 

 Alluvial soils are found near rivers in all sections of the country. 

 The most extensive alluvial soils are those near the Mississippi 

 River and its tributaries, especially the Red River, the Arkansas, 

 and the Missouri. 



Fig. 18. Alluvial cones, Wyoming. 



Glacial Soils. A glacier is a river of ice. It carries upon its 

 surface and within its mass, soil and rock fragments derived from 



