SOIL EEOSIOInT in THE SOUTH. 9 



localities, which will be described later, show the predominating 

 influence of some other factor. 



THE NATURE OF EROSION. 



The erosion of the soil occurs mamly in two ways which are mark- 

 edly different (1) as sheet erosion and (2) as the gully type of erosion. 

 In sheet erosion the water falling on the surface of the soil carries off 

 with it a small amount of soil material from every part of the field. 

 In advanced stages there appear incipient gullies, parallel to each 

 other, known as shoestring gullies. This type of erosion is not so 

 destructive of the field on which it occurs as the gully type, for the 

 removal is more miiform and, if a field is continually cultivated the 

 physical evidence of erosion may be sHght. A common result is the 

 occurrence of a rounded knoll showing a difference in the character 

 of the soil on the top and at the base, and often this difference extends 

 to a difference in productiveness, the top of the knoll being less 

 productive than the base. This type of erosion in advanced stages 

 develops gullies with sloping sides and rounded edges. It is often 

 spoken of as old-field erosion of parallel gully type. 



The region in western Virginia extending to the Tennessee line 

 conunonl}' erodes in this manner. In some sections the soU wash is 

 not serious enough to interfere with the cultivation of rather steep 

 hillsides without contouring or terracing. However, on bare fields 

 which remain out of cultivation for a few j^ears, the gullies form and 

 grow to considerable size. In eastern Tennessee the washing of the 

 soil is somewhat greater, but here, even in the hills, terraces are 

 hardly known. This same sort of erosion occurs in the Appalachian 

 region of Xorth Carolina and South Carolina and in northern Georgia 

 and Alabama, but in the last-named vStates the formation of gullies 

 is more rapid and the destruction greater. 



The second type of erosion, or the gullying, develops where, owing 

 to the occurrence of natural depressions, the water runs off in the 

 form of streams. These cut into the soil and soon develop gulches of 

 great depth with nearly vertical sides, which grow m length, breadth, 

 and depth with every rain. This type of erosion is the most difficult 

 to check, and renders the land on which it occurs practically valueless. 



RESULTS OF EROSION. 



Exressive erosion n^sults in a change in tlie ])1iysi('al condition of 

 the soil. As already pointed out, the bodily removal of soil particles 

 takes place from the surface. There is a sorting of the soil partich^s, 

 the larger and heavier being deposited first and the smallest last. TJie 

 result is an ini])uir('d physical condition of the s(h1 wherever this sort- 



74wr— liull. 180— 1&---2 



