74 SOILS: PROPERTIES AND MANAGEMENT 



formation, largely through natural weathering agencies. 

 This is really a phase of geochemistry, particularly as 

 regards those tints that originate from the oxidation of 

 the iron. Color has long occupied the attention of 

 geologists and agriculturists, in the first place because 

 it gives a clew to the mode of soil formation, and in the 

 second place because it is to a certain extent an index to 

 agricultural value. At the outset it must be understood 

 that soil colors are not pure colors, although spoken of 

 as such, but tints and shades. In soils it is possible to 

 find almost any conceivable color, ranging from white 

 sands to black swamp muds or the blood-red clays of the 

 Piedmont region. The three coloring matters of soil 

 may be classified as (1) the color arising from the mineral, 

 (2) the color given by the humus present in the soil and 

 around the particles, and (3) the reds or the yellows due 

 to oxidization of the iron. These three primary, or 

 basal, colors may be represented for convenience as 

 follows : 



Wtt/TE 



BLACK 



FIG. 9. A triangular representation of the three primary soil colors 

 and their mixtures. 



