BULLETIN OF THE 



ORIGIN OF SOILS. 



Mechanical and chemical disintegration of rocks. 



Mineral composition of important crystaline rocks. 



Chief rock-forming minerals. 



Quartz, the Feldspars, Mica, Hornblende, Augite, Talc 



(Serpentine.) 



Calcareous Spar or Calcite, Dolomite, Gypsum, Apatite. 

 Decomposition of these by atmospheric agencies; Water, 



Carbonic Acid, Oxygen, Ammonia. 

 Quartz soluble and insoluble forms. 

 Feldspars formation of clays and carbonates. 

 Hornblende and Augite formation of ferruginous clays, 



loams, carbonates. 

 Mica difficult to decompose. 



Sedimentary rocks Sandstones, shales, limestones, how formed; 

 their composition. 



Character of soils derived from these several rocks. 



Feldspar the source of potash. 



Apatite that of phosphates. 

 Decomposition greatly accelerated by pulverization, 



Effects of frost on rocks, 



Mechanical Attrition. 



Mechanical processes active in soil formation. 

 Action of flowing water. 



Action of water charged with sand and gravel. 

 Action of glacier ice. 



COMPOSITION OF SOILS. 



General Soil Ingredients are 



Unaltered Eock-powder. 



Altered Eock-powder. 



Clay. 



Vegetable matter. 

 According to the proportion of these they may be classed as 



LIGHT SOILS HEAVY SOILS 





Sandy, Humous. Clayey, Siliceous. 



Definition of these terms. 



Great diversity of sub-classification, adapted to local circum- 

 stances, and locally very important. 

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