CHAPTER II. 



CLASSIFICATION AND PHYSICAL PROPERTIES OF SOILS. 



A. KINDS AS TO DEPOSITION. 

 I. Sedentary, or Residual, Soils. 



These are formed where they lie by the weath- 

 ering of the rocks which underlie them. They 

 consist of those parts of the decayed rock which 

 are not easily dissolved and carried away by 

 rains. 



These soils vary in depth. In certain local- 

 ities the soil is only about seven feet thick, and 

 poor in soluble compounds, such as lime. "In 

 some parts of our Southern States the felspathic 

 rocks are often found thoroughly disintegrated 

 to the depths of 50 to 100 feet." * 



The nature of residual soils depends upon 

 the kind of bed-rock underlying them and the 

 weathering. " Thus, limestones make the rich 

 Blue-grass Region of Kentucky, and sandstones 

 make the poorer part of the State." f 



True soil, usually darker in color on account of 

 the vegetable mould which it contains, and of the 

 "oxidation and hydration of its minerals," forms 

 the surface layer. Below it is the subsoil, which 

 is often divided into layers, and which some- 



* Scott's Geology, p. 77. 



\ Gilbert and Brigham, Physical Geology, p. 87. 



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