GEOLOGICAL CLASSIFICATION OF SOILS 



38 



AeKANSAS LIMBSTON33 AND ITS ReSIBUAL ClaY ^ 



SiOa 

 AI2O3 



MnO 

 CaO 

 MgO 

 E2O 



NasO 

 CO2 



Feesh Rock 



Clay 



4.13 



33.69 



4.19 



30.30 



2.35 



1.99 



4.33 



14.98 



44.79 



3.91 



.30 



.26 



.35 



.96 



.16 



.61 



34.10 



.00 



Peecentage 

 Lost 



,00 



89.56 

 57.59 

 98.93 

 89.38 

 66.36 

 53.26 

 100,00 



The vast age of such soils tends to bring about great 

 oxidation, so that most of the iron has changed to hematite 

 and Umonite. Since almost all soils contain considerable 

 iron, the prevailing colors of residual soils are reds and 

 yellows, depending on the degree of oxidation and hydra- 

 tion. Grays and browns may exist, however, where iron 

 has been lacking or oxidation has been feeble. In texture 

 such soils usually present very fine conditions. Having 

 been attacked by both the physical and the chemical 

 agencies, the particles have been reduced to a very fine 

 state of division. Over residual areas the heavier soils 

 predominate, as silts, silt loams, clays, and clay loams. 

 Very often sand or chert may be present, having been a 

 constituent of the original rock mass. 



An examination of the particles of a residual soil usually 

 shows them to be in an advanced stage of decay. The 

 feldspars have lost their luster and have become opaque. 

 The iron has become oxidized, and the soluble bases have 



1 Penrose, R. A. F. 

 Vol. I, p. 179. 1890. 



Ann. Kept. GeoL Survey Arkansas, 



