CHAPTER III 



THE GEOLOGICAL CLASSIFICATION OF SOILS 



Weathering must be considered as affecting soils both 

 in situ and in motion. This gives two general classes of 

 materials — those that have not been shifted far from 

 their place of origin, and those in the formation of which 

 the transporting agencies have been instrumental. These 

 two general groups, designated as sedentary and trans- 

 ported, 1 are subject to considerable subdivision, as 

 follows : — 



Residual 



Sedentary 



Cumulose 



Transported 



Gravity — Colluvial 

 [ Alluvial 



Water I Marine 



I Lacustrine 



Ice — Glacial 



Wind — iEolian 



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

 areas of our arable regions and comes from many kinds of 

 rocks. Residual soils are old soils, the oldest with which 

 we have to deal in agricultural operations. Since a 



1 See Trowbridge, A. C. A Classification of Common Sedi- 

 ments. Jour, of GeoL, Vol. 22, No. 4, pp. 420-436. 1911. 



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