8o SCIENCE AND SOIL 



with the depth, the disintegrating bed rock being found at 4 to 10 

 feet beneath the surface. The bed rock and some of the pieces found 

 in the soil and subsoil consist of impure limestone. The soil is 

 commonly recognized as drift, but it is certainly much modified by 

 the residual material, and in places there is but little evidence of 

 glacial or loessial deposit. 



Sand, swamp, and bottom lands. In the older formations, as in 

 the Illinoisan glaciations and still farther south, the soil of the 

 smaller river bottoms is chiefly a deep gray silt loam; while, in the 

 more recently formed great soil areas, the principal bottom land 

 soil is a brown loam. In both cases the bottom land resembles 

 somewhat the top soil of the adjoining upland (which has con- 

 tributed much to its formation) , modified by additions of humus 

 and alluvium from other sources. Many other types of bottom land 

 are also found, but usually they are less abundant. 



Extensive swamp regions are found in most of the Northern 

 States, especially in Michigan, Wisconsin, and Minnesota, and in 

 the northern parts of Ohio, Indiana, Illinois, and Iowa. These 

 swamp soils vary almost from pure sand to pure clay, and almost 

 from 100 per cent mineral matter to 100 per cent organic matter; 

 and they also vary from moderately acid soils to marls containing 

 more than 50 per cent of calcium carbonate, and not infrequently 

 magnesium carbonate is present in sufficient amount to render the 

 soil non-productive and place it in the alkali class. These different 

 constituents vary quite independently, sand, peat, clay, peaty sand, 

 sandy peat, peaty clay or clayey peat (muck), sandy clay, clayey 

 sand, loam, sandy loam, clay loam, and peaty loam being among the 

 possible soil types; and any of these may be acid or may contain 

 " alkali." In addition we find such variations as deep peat, medium 

 peat, and shallow peat, with sand or clay or sandy clay subsoil. 

 In places there are broad, level, and very uniform areas of deep 

 peat, of peat on sand, or of nearly pure sand; and in other places 

 peat bogs and sand ridges alternate every few rods. Not infre- 

 quently sand dunes (still subject to more or less wind action) are 

 found in or adjoining these swamp regions; and in some sections 

 there are more extensive sand regions, including considerable 

 parts of counties in Ohio, Indiana, Illinois, and Wisconsin, and an 

 area of several counties in the north central part of the lower 

 peninsula of Michigan. 



