18 BULLETIN 180, U. S. DEPARTMENT OF AGRICULTURE. 



Carolina, northern Georgia, and central Alabama. It is in this 

 Piedmont Plateau that the greatest difficulty is experienced in deal- 

 ing with soil erosion. 



GEOLOGY OF APPALACHIAN AND PIEDMONT REGIONS. 



The soils are mainly residual, i. e., derived from the underlying 

 consohdated rocks. The rocks are of three classes: Old igneous, as 

 diorite, diabase, and granite; old metamorphic igneous and sedi- 

 mentary, or gneiss, schist, phyUite, and slate ; or young sedimentary^ 

 as Triassic sandstone, conglomerates, and shales. 



SOILS. 



Since the soils of these provinces are mainly residual, they are 

 comparatively uniform. The subsoils are nearly always heavy clay, 

 and the surface soils are often lighter in texture. Sandy loams, clay 

 loams, and clays occupy by far the greater part of the province. 



Where the subsoil is heavy clay, erosion is not so rapid as in the 

 soils with lighter subsoils. This is noticeable in portions of western 

 Virginia, western North Carolina, and eastern Tennessee, in the Appa- 

 lachian Mountain province. The erosion begins in Httle depressions 

 which gradually deepen, forming gulhes with sloping banks and 

 rounded edges, as shown in Plate V, figure 1. This is entirely a sur- 

 face erosion and easily controlled if properly handled. In the 

 mountainous regions terracing is not generally practiced, although 

 without a doubt such a system would prove beneficial. 



The Piedmont province of these States and of South Carolina, 

 Georgia, and Alabama suffers more from erosion than the regions 

 of higher altitudes. Especially is this true near the "Fall Line." 

 And in this province also the subsoil is often sandy and less tenacious, 

 so that when a gully forms the sides cave in. The erosion then often 

 proceeds by the caving in of the walls at the head of the gully, so 

 that, in advanced cases, there are formed extensive gulches with 

 almost perpendicular sides. This form of erosion is illustrated in 

 Plate V, figure 2. 



The most important soils throughout the Piedmont country belong 

 to the Cecil series, the Louisa soils probably ranking next in impor- 

 tance. These soils are mainly red and gTay and have clay subsoils. 

 The main differences in the series are that the Louisa soils are less 

 productive and have more micaceous subsoils than the Cecil. This 

 micaceous character increases their susceptibihty to erosion. 



The erosion in the Piedmont province is apparently more pro- 

 nounced in the more southerly States. This is probably due largely 

 to the climatic conditions. During the winter the temperature is 

 not low enough to cause deep freezing, and cold periods are of short 

 duration. The formation of ice crystals at the surface of the soil 

 raises a thin layer, and when the ice melts there remains an inch or 



