CHAPTER II 

 ORIGIN AND COMPOSITION OF SOILS 



Origin of Soil Geologically Considered Chemical Elements 

 Present Non-metals M etals 



THE term soil, in its broadest sense, is used 

 to designate that portion of the surface of the 

 earth which has resulted from the disintegration 

 of rocks and the decay of plants and animals, 

 and which is suited, under proper conditions 

 of moisture and temperature, to the growth of 

 plants. It consists, therefore, chiefly of min- 

 eral substances, together with some products of 

 organic life, and of certain living organisms 

 whose activity may influence vegetable growth 

 either favorably or otherwise. The soil also holds 

 varying quantities of gaseous matter and of water, 

 which are important factors in its functions. The 

 soil cannot be regarded as entirely dead matter, 

 but as containing living organisms exhibiting 

 many most remarkable biological phenomena. 



Agriculturally considered, the soil proper is the 

 older and more thoroughly disintegrated super- 

 ficial layer of the earth, which has been longest 

 exposed to weathering and the influences of 

 organic life. It varies from a few inches to several 



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