54 SOILS: PROPERTIES AND MANAGEMENT 



This close resemblance to the parent rock is not sur- 

 prising, since glacial soil is ground-up rock material of 

 recent formation on which the weathering agencies have 

 as yet had little time for action. Therefore the amounts 

 of the important constituents in such soil are governed 

 largely by the composition of the original rock. The 

 lime content is due to such a relationship, and the agri- 

 cultural value of the soil is greatly influenced thereby, 

 since large amounts of calcium are of great importance 

 to soil fertility. The hill soils of central New York 

 (Volusia series) come from shales poor in lime, and the 

 soil owes its properties very largely to this lack, which 

 is traceable to the parent rock. On the other hand, cer- 

 tain glacial soils of the Mississippi Valley (Miami series) 

 formed from sandstones and limestone, contain plenty 

 of lime due to the nature of their rock origin. Glacial 

 soils from limestone always contain plenty of lime, a 

 condition that is far from true with residual soils. 



41. Humus of glacial soils. The humus content of 

 glacial soils depends to a large extent on the climatic 

 conditions under which the soil has existed since its 

 formation. If environmental factors have been such 

 as to encourage the accumulation of organic matter, 

 these soils will exhibit the deep black color that arises 

 from the presence of such material. If, however, con- 

 ditions do not encourage the natural growth of a heavy 

 vegetation, the amount of organic matter in such virgin 

 soil will be low. Lime may be a very great factor in 

 such soils, not only in the encouragement of plant growth, 

 but also in the proper decay of the plant tissue after 

 it has become incorporated with the soil. 



Glacial till soils are found distributed over all the area 

 north of the great terminal moraine, and stretch, roughly, 



