CHAPTER II 



SOIL-FORMING PROCESSES 



After the first proper estimate of the relations between 

 the crop and the soil, the next step is toward the mode of 

 soil formation and the agencies concerned. As might be 

 expected, this is a complicated problem from the fact 

 that most rocks are so heterogeneous in their composition. 

 The question becomes still further involved because of 

 the many factors that are continually fmictioning in rock 

 decay. This process of the breaking down of rock masses 

 and their gradual evolution into soil is called weathering.^ 

 Rock weathering may be defined specifically as the changes 

 that rock masses undergo due to the physical and chemical 

 activities of atmospheric agents. Everything on the 

 earth^s surface is seeking a more stable condition, and 

 therefore, from a geological standpoint, is continually 

 changing. If a soil represents a more stable condition 

 than the exposed rock, the rock slowly evolves toward 

 the soil. Again, if a soil presents constituents not wholly 

 stable, that soil will change by an elimination or an 

 alteration of these components. The soil, then, is a 

 geologic unit. It is a transition product from one con- 

 dition to another. 



This weathermg, which brings about such changes and 

 is such a factor in the modifications of our topography, is 



1 For a complete discussion of weatiiering, see Merrill, G. P. 

 Rocks, Rook Weathering, and Soils. New York. 1906. 



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