GEOLOGICAL CLASSIFICATION OF SOILS 57 



cial soils from limestones generally contain plenty of lime, 

 a condition that is far from true with residual soils. 1 



The organic 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 mat- 

 ter, these soils will exhibit the deep black color that arises 

 from the presence of such material. If, however, conditions 

 do not encourage the natural growth of a heavy vegetation, 

 the amount of organic matter in such virgin soil will be low. 

 Lime and other nutritive elements may also be a great factor 

 in the development of vegetation on these soils. Glacial till 

 soils are distributed over all the area north of the great 

 terminal moraine, and stretch, roughly, from New Eng- 

 land to the Pacific coast. They comprise a great variety of 

 soils, differing not only in their physical characters, but also 

 as to fertility. They are adapted to many crops, but general 

 farming is practiced on them to the greatest degree. This 

 means extensive, rather than intensive, operations. In some 



1 Partial Analyses of Soils from the Limestone Driftless and 

 Glacial Region of Wisconsin 2 Are of Interest in This Regard : 



Constituents 



Residual 



Glacial 



Si0 2 



A1 2 3 + Fe 2 



MgO 



CaO 



K 2 G 



P 2 B 



CO a 



71.13 

 18.02 

 .38 

 .85 

 1.61 

 .02 

 .43 



49.13 



31.12 



1.92 



1.22 



1.61 



.04 



.39 



40.22 

 11.30 



7.80 

 15.65 



2.36 



.05 



18.76 



48.81 

 10.07 



7.95 

 11.83 



2.60 



.13 



15.47 



2 Chamberlain, T. C. and Salisbury, R. D., The Driftless Area of the 

 Upper Mississippi; Sixth Ann. Rep. U. S. Geol. Survey, pp. 249-250, 1885. 

 These analyses illustrate to very good advantage the beliefs entertained 

 by Chamberlain and Salisbury regarding the differences between residual 

 and glacial clays. Residual clay is designated by them as "rock rot," 

 and glacial clay as ' ' rock flour. ' ' The latter, being less weathered, "re- 

 tains a larger proportion of its easily soluble materials. 



