38 CHEMISTRY, GEOLOGY 



woody fibre of vegetables, as hay, straw, corn- 

 stalks, etc.. in the form of manure. 



The inorganic or incombustible part of the 

 soil is derived from the gradual crumbling down 

 of different kinds of rocks. The decaying walls 

 of buildings, the substance called rotten rock, 

 which is trap or whinstone in a decomposed state. 

 limestone, gravel, etc., are also sources which 

 supply inorganic matter to the soil. 



Rocks consist, to a large extent, of sandstones, 

 limestones, and clays. Of the sandstones, there 

 are the red, and the white, and other freestones. 

 Limestones include chalk, gypsum, the blue, 

 and other varieties. Clays comprise the skte 

 used for roofing, and the shale or shiver of the 

 coal beds. All the inorganic part of soils main- 

 ly consists of sand, clay, and lime. 



Sometimes soil contains one of these substanc 

 in a much larger quantity than either of the 

 others. When sand is most abundant, the land 

 is called .<*andy soil. If the clay greatly pr 

 dominates, it is a stiff, or clay soil. If the lime 



Questions. Whence does the soil derive its inorganic 

 part ? Of what do rocks chiefly consist ? Name some 

 the varieties of sandstones. Of limestones. Of clays 

 When soil contains most sand, what is it called ? Wh 

 when clay is most abundant ? 



