SOIL-FORMING PROCESSES 



29 



As shown by the diagrams, the soil from the granite does 

 not differ greatly from the original rock, except in loss 

 of bases, assumption of water, and increase of organic 



Fig. 2. — Diagram showing the chemical composition of Virginia lime- 

 stone and its residual clay. See analyses above. 



matter. The residual clay from the limestone presents 

 greater differences, due to the almost entire disappear- 

 ance of calcium carbonate. The diagrams for the two 

 clays resemble each other fairly closely in spite of their 

 widely differing sources. Because weathering causes 

 the persistence and accumulation of silica, aluminium, 

 and iron, and a loss of the basic materials, all soils as 

 they weather tend to approach a similar composition. 

 Yet, owing to a difference in the adjustment of the forces 

 at work and in the time element, no two soils will ever 

 be exactly alike. Soils will differ, then, from the original 

 rock and from one another according to the intensity 



