32 THE SOIL SOLUTION 



siderations there can be but little doubt that they exist in the 

 clays as in the coarser separations. 1 



The minerals to be anticipated in the soil are those commonly 

 occurring in the rocks; but as a result of the action of mixing 

 and transporting agencies, a soil normally contains minerals from 

 rocks other than those from which it is primarily derived. 



It would hardly be fair to regard a beach sand, for instance, as 

 a normal soil. Yet it is surprising how many minerals other 

 than quartz can usually be found even in a beach sand. 

 Opinions may differ as to just what are the common rock- form- 

 ing minerals, and perhaps no two mineralogists or petrographers 

 would give identical lists, but there are a number of minerals 

 which would appear undoubtedly in every list, and these would 

 be found generally in any soil. Again, it might happen that in 

 any given sample of soil, no pyroxene, for instance, could be 

 found; but experience shows that it would never happen in such 

 a case that no amphibole, chlorite, serpentine, or other ferro- 

 magnesian silicates would be present. However distinct these 

 minerals cited may be from each other morphologically or 

 optically, they are much the same in their chemical character- 

 istics, their solubilities and their reactions with water and such 

 dilute solutions as exist in the soil. Hence from the point of 

 view of the soil chemist they may be considered for all practical 

 purposes varieties of one and the same mineral species. Con- 

 sequently an important result of researches on the minerals of 

 the soil is the generalization that soils are far more heterogeneous 

 than are rocks, and that practically every soil contains all the 

 common rock-forming minerals. 3 



It is not difficult to account for the heterogeneity of the mineral 

 content of the soil. Many of our rocks are reconsolidated soils, 



1 See, The mineral composition of soil particles, by G. H. Failyer, 

 J. G. Smith and H. R. Wade, Bull. No. 54, Bureau of Soils, U. S. Dept. 

 Agriculture, 1909. Recent improvements in microscope methods make it 

 possible to identify without serious trouble the mineral content of silts 

 with a diameter as low as 0.005 mm., and many even of the clay, particles 

 have recently been determined with satisfactory accuracy. 



* See Bull. No. 30, Bureau of Soils, U. S. Dept. Agriculture, 1905, 

 p. 9. 



