76 



NATURE AND PROPERTIES OF SOILS 



ency together with the formation, as weathering proceeds, 

 of the fine coloidal-like epidote, chlorite and similar groups, 

 should in general keep the percentage of minerals other than 

 quartz higher in the finer portions of a soil. 1 The following 

 data sustain this assumption: 



Table XII 



MINERALS OTHER THAN QUARTZ IN THE SANDS AND SILTS OF 

 VARIOUS SOILS 2 



It is to be seen immediately that in every case the silt car- 

 ries a large quantity of the important soil-forming minerals 

 and a smaller amount of quartz than does the sand. This re- 

 veals at least one of the reasons for the greater fertility and 

 lasting qualities of fine-textured soils as far as agricultural 

 operations are concerned. It is important to note, however, 



1 A petrographic analysis as now developed is very unsatisfactory as it 

 throws practically no light on the character of the clay group because 

 of the extreme fineness of this material. Even for silt the results are 

 unsatisfactory and difficult to express quantitatively. The correlation 

 of a petrographic analysis and productivity is vague. 



a McCaughey, W. G., and Fry, W. H., The Microscopic Determina- 

 tion of Soil-forming Minerals; U. S. Dept. Agr., Bur. of Soils, Bui. 91, 

 1913. See also, Plummer, J. K., Eelation of the Mineralogical and 

 Chemical Composition to the Fertility Requirements of North Carolina 

 Soils; N. C. Agr. Exp. Sta., Tech. Bui. 9, 1914. Plummer, J. K., 

 Petrography of Some North Carolina Soils and its Relationship to their 

 Fertilizer Requirements; Jour. Agr. Res., Vol. V, No. 13, pp. 569-581, 

 1915. Robinson, W. O., The Inorganic Composition of Some Important 

 American Soils; U. S. Dept. Agr., Bui. 122, Aug., 1914. Shorey, F. C, 

 et ah, Calcium Compounds in Soils; Jour. Agr. Res., Vol. VII, .No. 3, 

 pp. 57-77. Jan., 1917. 



