CLIMATIC AND GEOCBEMICAL RELATIONSHIPS 71 



Von Engeln/ in a comparison of glaciated soils with 

 corresponding residual areas, was able to point out cer- 

 tain general differences. The agricultural condition 

 within the zone of glaciation w^as always consistently 

 higher than that beyond the regions of drift accumulation. 

 The extensive leveling due to glacial erosion and dep- 

 osition had almost always resulted favorably for agri- 

 cultural operations. Even the thickness of the drilt 

 was found to conserve the ground water supply. Not 

 only did this author conclude that glacial soils were 

 richer in soluble plant-food constituents than residual 

 soils, but he also showed that glacial soils had a greater 

 crop-producing power and a higher agricultural value. 

 The dominant textural quality of glacial soils seems 

 adapted to certain staple food crops, and, due to their 

 intermingling, a considerable opportunity for diversified 

 and intensified farming is offered. It is therefore evident 

 that in any study of soils, particularly those of the United 

 States, a careful consideration of the effects of glaciation 

 is necessary. The great ice sheet has been responsible 

 in some cases for the rejuvenation of our soils, in others 

 for the production of an entirely new soil mantle. Even 

 the alterations in topography are factors not to be ignored. 



55. Arid and humid soils.^ — This distinction between 

 soils due to differences in the formative process is always 

 evident, but is particularly striking in a comparison of arid 

 and humid regions. In areas of light rainfall the physical 

 agents are dominant, and disintegration goes on very 

 largely without decomposition. Under humid conditions, 



1 Von Engeln, 0. D. Effects of Continental Glaciation on Api- 

 culture. Bui. Amer. Geog. Soc, Vol. XLVI, pp. 353-355. 1914. 



^ For a more complete discussion of this subject, see Hilgard, 

 E. W. Soils, Chapters XX and XXI, New York. 1911. 



