13 



higher slopes and has accuinulated faster than the sluggish streams can 

 remove it. Some of the type, however, is lacustrine in origin, having 

 been deposited in shallow basins or ponds. A very small part of it can 

 be attributed to stream and river overllows." ( )riginally it was almost 

 exclusively grass-laml. 



Marshall loam, designated Marsliall sill ktani in counties more re- 

 cently surveyed, is derived from the weathering of loess deposits 

 (11, p. 35). The surface soil is a yellowish brown or brown silty 

 loam to 6 or 12 inches, under which is a compact yellow silty loam 

 and under this, at a depth varying from 24 to 36 inches, a loose 

 incoherent silty material lighter in color. The loess deposit varies from 

 a few inches to 1.^ feet in thickness and iii this county is underlain 

 by glacial material. 



The mechanical composition of typical samples from the county 

 reported by Burke and Kolbe (11) is given in table 1. These show 

 the Carrington loam to be coarser in texture than the three silt loams, 

 having considerably less of particles as fine or finer than very fine sand 

 and accordingly more of the coarser fractions. The finer fractions 

 of the silt loams constitute from 81.6 to 94 per cent of the surface soil 

 and from 68.9 to 91.4 per cent of the subsoil, while for the loam they 

 form only 76.2 and 68.5 per cent for soil and sul^soil, respectively. The 

 mechanical composition of the subsoil of the kargo silt loam is very 

 similiar to that of the Carrington loam. 



Table i. — Mechanical composilion of typical sainpL's from Rice County, as 

 reported by Burke and Kolbe. 



The great amount of time consumed by a mechanical analysis pre- 



