CLASSIFICATION AND PROPERTIES OF SOILS. 45 



in the kind of rock material as well as in its 

 state of disintegration. " The soils of the cen- 

 tral valley of California have mainly come down 

 from the Sierras by the wash of the rivers. The 

 soils of Louisiana have been brought from the 

 Rocky Mountains, from the great plains, from 

 the prairies, and from the plateaus and moun- 

 tains of the Appalachian region. They have 

 been transferred by the Mississippi and its 

 branches. The earthy mantle of Connecticut 

 and Rhode Island is in part composed of rock 

 flour and stones brought from Massachusetts 

 and the northern New England States. The 

 Connecticut and other rivers have done some of 

 this work, but much more is due to the great 

 glacier moving south over that region." 



B. KINDS OF SOIL AS TO DERIVATION. 



As has been said, the basis of soils is disin- 

 tegrated rock. Hence, the physical and chem- 

 ical properties of soils depend upon the geolog- 

 ical formation of the mass of rock from which it 

 is derived. 



If a deposit of quartz (SiO 2 ), which it is esti- 

 mated composes one-half of the rocks of the 

 earth, has been slowly disintegrated it will result 

 in hard, distinct grains of sand, since quartz dis- 

 integrates with difficulty. 



Gilbert and Brigham, Physical Geology, p. 87. 



