40 THE PRINCIPLES OF SOIL MANAGEMENT 



subject to mechanical sorting by wind and water, in 

 addition to the fact that no single element has come 

 through without loss. 



The figures in the first column of each pair show the 

 proportionate loss of each constituent. The second 

 column shows what would be expected, viz., that the 

 elements present in largest amount would be subject 

 to the largest total loss. But the first column shows 

 that certain elements are more weak chemically than 

 others. These elements are lime, magnesium and the 

 alkalies. While the figures are limited, still phosphoric 

 acid appears to be subject to a large loss. There is almost 

 invariably the assumption of water, and frequently of 

 carbon dioxid, indicating alterations in chemical com- 

 binations which, while freeing some elements, may render 

 others more resistant. 



The striking change in the physical properties of a 

 residual soil from the parent rock depends in part upon 

 this unequal loss of elements. As a rule, unweathered 

 residual soils are highly colored, usually red or yellow. 

 This results from the accumulation and alteration of 

 the iron. Hence, a gray limestone will produce a dark 

 red clay. Other properties, as the texture, result in the 

 same way. Any very refractory material, as chert in 

 limestone or quartz in igneous or secondary rocks, 

 is likely to persist and remain scattered through the 

 soil. The cherty hills of Tennessee and the Ozarks are 

 examples of the former, and the topography of the coun- 

 try is largely determined by the accumulation of this 

 material. Some of the stony soils of the Piedmont 

 regions are examples of the second type of soils. The 



