SOIL EROSION 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 mainly 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 uniform and, if a field is continually cultivated the 
physical evidence of erosion may be slight. 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 
commonly erodes in this manner. In some sections the soil 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 years, 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 North Carolina and South Carolina and in northern Georgia 
and Alabama, but in the last-named States 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 in 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. 
Excessive erosion results in a change in the physical 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 particles, 
the larger and heavier being deposited first and the smallest last. The 
result is an impaired physical condition of the soil wherever this sort- 
74681°— Bull. 180—15 2 
