GEOLOGICAL STUDY OF SOILS 



57 



action of water is illustrated in the workings of large 

 rivers where the pulverized rock particles are deposited 

 along the river and at its mouth. Large areas of the 

 soil in valleys and river bottoms have been formed in 



FIG. 20. Granite Bluff shattered by Frost. 

 (Minnesota Geological and Natural History Survey.) 



this way, and in most cases these soils are of high fertil- 

 ity. The action of water is not alone confined to form- 

 ing soils along water courses, but is equally prominent 

 in the formation of soils remote from streams or lakes, 

 as in the case of soils deposited by glaciers. 



57. Glacial Action. At one time in the earth's history, 

 the ice fields of polar regions covered much larger areas 



