SOILS OF THE EASTERN UNITED STATES AND THEIR USE VIII. 



THE CLARKSVILLE SILT LOAM. 



GEOGRAPHICAL DISTRIBUTION. 



The Clarksville silt loam is one of the most extensive of the upland 

 limestone soils, being exceeded in area only by the Clarksville stony 

 loam. The Clarksville silt loam has been encountered in 15 different 

 soil survey areas, located in 5 States and the total extent of the type 

 already mapped amounts to 1,599,938 acres. It thus constitutes an 

 extensive and important type of soil in the localities where it occurs. 



CHARACTERISTICS OF THE SOIL AND SUBSOIL. 



The surface soil of the Clarksville silt loam to an average depth of 

 about 8 inches consists of a gray, yellowish-gray or pale-yellow silty 

 loam. In many areas this surface soil is rather compact and dense, 

 but in the better tilled areas it is usually mellow and friable. The 

 immediate subsoil from a depth of 8 or 10 inches usually to a depth 

 of nearly 3 feet is a heavy yellow or reddish-yellow silt loaro, which 

 grades downward into a stiff compact silty clay at a depth of 3 feet 

 or slightly more. In some cases the entire 3-foot section is marked 

 by gray or yellow colors, but in the vast majority of areas the deeper 

 subsoil becomes reddish yellow or a deep red in color. In general 

 there is only a small quantity of chert or flint in the surface soil, but 

 in the subsoil there are bands and layers of chert as well as scattered 

 chert fragments, which in many instances notably assist in the sub- 

 soil drainage of the type. The deep subsoil usually rests upon the 

 surface of the limestone rock from which the soil is derived by partial 

 solution. 



In all cases the Clarksville silt loam is derived from cherty and im- 

 pure limestones, usually of the Carboniferous age, although practi- 

 cally all of the limestones containing bands, layers, and lenses of 

 chert may give rise to this type, and there are areas where limestone 

 interbedded with thin layers of fine-grained sandstone has also 

 formed the original rock from which the Clarksville silt loam was 

 formed. 



The Clarksville silt loam differs from the other members of the 

 same series in possessing a uniform soft silty surface soil, which gradu- 

 ally becomes more dense and compact with increasing depth. The 



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