20 GEOLOGY OF SOIL. 



the proof of this principle, that rocks do not affect 

 the vegetation which covers them. 



29. The space which has thus been surveyed, 

 presents amid great diversity of rocks, a singular 

 identity in chemical composition of the soil. These 

 facts lead to the third principle of agricultural chem- 

 istry, ROCKS HAVE NOT FORMED THE SOIL WHICH 

 COVERS THEM. 



30. Everywhere, with the exception of the tops 

 of some mountains, the rocks of the globe are cov- 

 ered, from a few inches, to some hundred feet in 

 depth, with gravel, sand, clay, rolled stones, some- 

 times alternately with each other, sometimes in con- 

 fused heaps. The best attested, and most univer- 

 sally admitted fact of geology, is, that the loose ma- 

 terials of our globe have been transported, from 

 a few, to many hundred miles from their original sit- 

 uation. With a few exceptions, the soil which now 

 covers rocks, has been derived from places distant, 

 and from rocks distinct, from those on which it now 

 reposes. This is peculiarly true of soil on limestone 

 districts, which does not contain more lime than the 

 soil reposing on granite. 



31. Transportation of soil, is a fact so well estab- 

 lished, that it needs only to be mentioned. There 



