P a O fl 



% K 2 



•109 



1-894 



•109 



1-918 



•094 



2-016 



•096 



2-099 



•095 



2-239 



•104 



2-155 



•101 



1-958 



Mineral Plant Foods contained in Soils. 355 



Illinois Soils — Hilly Uplands — Surface Soil, 0-7" — 

 Yellow Silt Loam. 



Soil Area or Glaciation 



Unglaciated 



Lower Illinoian 



Middle " 



Upper " — 



Pre-Iowan 



Iowan 



Early Wisconsin 



Yellow-gray Silt Loam — Undulating Upland. 

 Late Wisconsin -093 2-867 



On the other hand, positions in an erosion cycle, held by 

 the deposits of the various glaciations, serve Racialists as 

 criteria for distinguishing between the glaciations. The exist- 

 ence of sluggish and obstructed drainage, a topography marked 

 by the presence of many small lakes, kettle holes, and wide 

 areas of swamp lands, are, in glacial regions, the earmarks of a 

 very recent advance. In localities where the glaciation is so 

 recent the drift sheet is practically continuous over the area. 

 The drainage has not yet had time to establish itself. It is a 

 region of youth in the development of an erosion cycle. Lev- 

 erett* compares the erosion and weathering of areas, with sim- 

 ilar original topography, in the Wisconsin and Illinoian glacial 

 deposits as follows : " In the Illinoian glacial drifts of western 

 Illinois approximately one-half the surface has been reduced 

 below the original level as a result of post-IUinoian glaciation, 

 drainage development ; while in the Wisconsin drift, post- 

 Wisconsin drainage has scarcely sufficed to reduce one-tenth its 

 original surface. In the Illinoian drift calcareous constituents, 

 pebbles as well as fine material, are nearly completely removed 

 to a depth of four to six feet by leaching, while weathering 

 often extends to two or three times these depths. In the Wis- 

 consin drift limestone pebbles are present at the top of the 

 bowlder clay, and leaching of fine calcareous material seldom 

 extends to more than a meter. The weathering is very slight 

 as compared to the Illinoian drift." These facts indicate a real 

 difference in the composition of the materials ; one that should 

 be reflected in the chemistry of their soils. 



Indeed, a very real difference exists in the actual produc- 

 tivity of the soils of the early and late glaciations, whether or 

 not it depends on the percentages of the mineral plant foods 



*Leverett, P., Weathering and Erosion as Time Measures, this Journal, 

 xxvii, pp. 356-7, 1909. 



Idem., Comparison of North American and European Glacial Deposits, 

 Zeitsohr. f. Gletcherkunde, iv, p. 332, 1909-10. 



