28 



SOILS: PROPERTIES AND MANAGEMENT 



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 wholly 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. 



Fig. 1. — Diagrammatic representation of the chemical composition of 

 fresh granite and its residual clay. See analyses above. 



