THE SOIL PARTICLE 77 



that, althougli quartz is the predominating mineral in sands, 

 all the common soil-forming minerals are usually accessory.^ 



It is interesting in passing to observe the diferenees ex- 

 hibited by the various soil provinces although the number of 

 samples shown by Table XII are far too small for definite 

 conclusions. The marine soils are particularly low compared 

 with the residual and glacial, due to the hard usage which 

 the soil material of the former has received. No significant 

 differences exist between the glacial and residual soils. The 

 arid soils, however, are markedly higher in the important min- 

 erals due to the suppression of chemical weathering and the 

 activity of the physical agents. The silica in such soils is 

 held as complex silicates, which carry the elements that are 

 so important in plant development. Although these data are 

 based on but a few samples, they are so concordant with what 

 would naturally be expected that these general conclusions 

 cannot be avoided. 



The mineralogical examination has revealed a larger per- 

 centage of such minerals as feldspars, mica, hornblende, and 

 the like, in the finer separates. A larger percentage of the 

 important nutrient elements would, therefore, be expected in 

 those groups. The following data,^ compiled from work per- 

 formed by the United States Bureau of Soils, substantiate this 

 assumption. (See Table XIII, page 78.) 



It is evident that the finer portions of soil are in general 



* Below is given the mineralogieal description of a loessial silt loam of 

 the Marshall Series from Missouri: Eobinson, W. 0., The Inorganic 

 Composition of Some Important American So4s; XJ. S. Dept. Agr., Bui. 

 122, Aug., 1914. 



Very fine sand — minerals other than quartz, 20 per cent. Orthoclase, 

 10 per cent. Muscovite, 2 per cent. Biotite, magnetite, epidote, albite, 

 labradorite, oligoclase, tourmaline, zircon, garnet, and augite are also 

 present. 



Silt— Minerals other than quartz, 34 per cent Orthoclase, 4 per cent. 

 Muscovite, 4 per cent. Biotite, magnetite, epidote, albite, labradorite, 

 oligoclase, tourmaline, rutile, glaueophane, hornblende, and augite are 

 also present. 



2 Failyer, G. H., and Others, The Mineral Composition of Soil Fartides; 

 U. S, Dept. Agr., Bur. Soils, Bui. 54, 1908. 



