65 



section shows nearl) twice as niiicli on the Kaii>an as oil the Late 

 Wisconsin. 



The organic carhon, huth in anionnt anil (hstrihntion, is very 

 similar from drift to drift with both of the Carrinj^^ton types, hut in 

 the first two sections of the Fars^o sih loam it is the higher on the 

 Kansan, in this resembling the volatile matter. The forested fields 

 show lower percentages than those on the grassland. 



The distribution of nitrogen resembles that of organ.ic carbon 

 and volatile matter. 



In relative darkness of color there is no difference between the 

 drifts in the case of any of the soil types, except in the surface six-inch 

 section on the Carrington loam and the second and third foot-sections 

 on the Fargo silt loam. \\\\h these the soil on the T.ate W^isconsin is 

 somewhat the darker. 



If the three types of soils studied in detail were to be classified 

 according to the Russian system, the Fargo silt loam would be con- 

 sidered a true chernozem, the Carrington silt loam a chernozem in 

 the early stages of degradation, and the Carrington loam a degraded 

 chernozem. 



In general, the first three feet of soil on the well-drained areas, 

 originally similar in topography and profile and later covered by the 

 same type of vegetation, are almost identical on the two drifts, which 

 would suggest that the age of the most recent glaciation is so great as 

 to have permitted the uniformity in climate and in vegetative cover, 

 which has prevailed on the two sides of the dividing line in any 

 locality, to almost completely obliterate the effects of the great differ- 

 ence in age. 



It appears probable that the previously reported marked differ- 

 ences in composition between the soils on the Kansan and on the Des 

 Moines Lobe of the Late Wisconsin are to be attributed to the effects 

 of the differences in climate and vegetation that are involved when 

 we employ data from large sections extending far to the east and to 

 the west, respectively, of the contact line of the surface ex|)osures of 

 the two glacial sheets. It is prol^able that the diff'erences which have 

 been induced by differences in precipitation and vegetation within the 

 area of any one glaciation may be found to far exceed those attribut- 

 able onlv to diff'erences in the age of glaciation. 



