56 NATURE AND PROPERTIES OF SOILS 



the forces of weathering, while they have had time to pro- 

 duce a soil from the material left by the ice, have not as yet 

 seriously depleted the essential constituents. The mineral 

 elements in such soils are governed to a considerable degree 

 by the composition of the original rock. Calcium content, 



Pig. 12. — ^Block diagram showing the relationsliip which sometimes exists 

 between glacial soils and the underlying rocks. Glacial movement 

 left to right. (After Emerson.) 



for example, is controlled largely by such a relationship. 

 The hill soils of southern New York (Volusia and Lords- 

 town) come from shales low in lime and their productive- 

 ness is seriously affected thereby. On the other hand, cer- 

 tain glacial soils of central New York and of the Mississippi 

 Valley (Ontario and Miami) have been formed from cal- 

 careous till and owe their productivity partly thereto. Gla- 



