390 



Sources of the Constituents of Minnesota Soils. 



and humid climates chiefly by waters of a comparatively high tem- 

 perature, in climates that are warm and dry, by sunshine and sud- 

 den changes of temperature; in cold climates, by moisture and 

 freezing. But with these forces, others naturally come into play ; 

 for instance, the erosion of rain water is necessary to remove the 

 loosened material, so that which lies below and still fresh, may 

 come within the influence of weathering agencies ; or the wind, 

 blowing through high arid regions with great violence, carrying 

 clouds of dust, constantly lays bare the surface of underlying 

 rocks and burrowing animals of many types constantly bring to 

 the surface quantities of fresh earth. 



The layers of soil sections. — In any normal soil section there 

 are three layers, (i) the soil; (2) the sub-soil ; (3) the underlying 

 rock. The soil is filled with the roots and rootlets of plants, and 

 the burrows of insects and worms. Plants are constant constitu- 

 ents of soils. Numerous fungi and plants of many a low type 

 abound. 



Figure i. The decomposition of limesione and the foundation 

 and accumulation of soil. This is representative of areas in 

 Southeastern Minnesota. Drawn by F. W. Sardeson. 



The sub-soil is a broken-up layer consisting of pebbles large 

 and small, some crumbling and others fresh, around which are 

 pushing their crooked ways the roots of trees and strong herbs. 

 In color this layer is like the rock beneath ; and while in general 



