CHAPTER III 



THE GEOLOGICAL CLASSIFICATION OF SOILS 



Weathering must be considered as affecting soils, whether 

 they are in motion or at rest. This gives rise to two general 

 classes of soil materials — those that have not been shifted 

 far from their original situation and those that have suffered 

 considerable translocation. These two general groups, desig- 

 nated as sedentary and transported, are subject to subdivision 

 as follows : x 



o ,1 * /Residual 

 Sedentary j Cumulose 



Gravity Colluvial 



f Alluvial 



Water . . . . i Marine 



[ Lacustrine 



Ice Glacial 



Wind ^Eolian 



Transported 



25. Residual soils. 2 — This group of soils covers wide 

 areas of arable regions, especially in the tropics and sub- 

 tropics, and comes from many kinds of rock. Residual soils 

 are, in the main, old soils, usually the oldest with which we 

 deal in agricultural operations, although some residual soils 

 are comparatively young. Since they are formed in situ, 



1 Merrill, G. P., Bocks, Bock Weathering and Soils, p. 288; New York, 

 1906. 



' For a full discussion of the origin and characteristics of the soils 

 of the United States see Marbut, C. F. et al., Soils of the United States; 

 U. S. Dept. Agr., Bui. 96. 1913. For the soils of the Southern States, 

 consult Bennett, H. H., The Soils and Agriculture of the Southern 

 States; New York, 1921. 



38 



