28 



SOILS: PBOPMETIBS AMD MANAQEMBWT 



Soils have resulted in both cases from the decay of 

 these rocks. In the case of the granite the resulting soil 

 was a deep red clay, with quartz grains present. The 

 soil from the limestone was a plastic clay, high in silica 

 and aluminium. Leaching has probably gone on to a 

 very great extent in both soils. It is noticeable also 

 that the basic constituents have suffered the greatest 

 losses, especially calcium, magnesium, sodium, and 

 potassium. The carbonate has almost w^hoUy disap- 

 peared from the limestone clay, showing that a limestone 

 soil may not necessarily be rich in lime. As a matter of 

 fact, the chances are that if it is residual it will be lacking 

 in that compound. When shown diagrammatically (See 

 Figs. 1 and 2), the changes that the parent rocks have 

 undergone chemically in forming a clay will become 

 apparent. 





li 







^"Pf 



Qi 























\ 



/ 







\ 











\ 





/(si 



,/ 



\ 



fgO 





\ 



V 









\ 







/^ 







O" 



/ 

 y 





\ 









\ 

















/ 











\ 













./ 











v 



J 





(a) /res/} roc/( 





f 









v- 



■'(4 





(b)a 



ki/ 







' *% 







Fia. 1. •— Diagrammatic representation of the chemical composition o 

 fresh granite and its residual clay. See analyses above. 



