20 BULLETIN" 180^ U. S. DEPARTMENT OF AGEICULTUEE. 



some places sandy, extending to a considerable depth. Where such 

 areas are forested erosion is slow, but with the removal of the forest 

 growth the erosion is very rapid. Any rut or path breaking through 

 the upper layer of heavy soil so(yn develops into devastating erosion. 

 In some places, owing to this condition, any attempt to cultivate 

 the soil should never be made. With plowing and clean cultivation 

 it is practically impossible to prevent erosion. In a few counties a 

 rough estimate places the eroded and abandoned areas at 25 to 33 

 per cent of the total. 



The great danger of losing large areas of valuable land is appre- 

 ciated in Tennessee, and under the direction of the State geologist 

 the best methods of preventing erosion and reclaiming eroded land 

 are being studied. Plate VIII illustrates the seriousness of the situa- 

 tion in some parts of the State. The main problem is to arouse the 

 farmers to a realization of the importance of treating their soil in 

 the maimer best suited to its condition. Soils that can not be 

 cultivated without danger of erosion should be used for the produc- 

 tion of hay, for pasture, or for forestry, either of which may pay 

 better under the circumstances than the crops obtained from clean 

 cultivation. 



In extreme western Termessee and Mississippi the deep silty soils 

 erode in a slightly different way. The soils of nearly uniform composi- 

 tion to a great depth are compact and the pore spaces are compara- 

 tively large, so that in their natural condition they absorb much of 

 the water falling on the surface. The surface soils and subsoils having 

 the same composition, the sides of cuts are vertical, with very little 

 tendency toward caving, such as occurs where the subsoil becomes 

 saturated and is washed out, leaving the surface layer without 

 support. The attrition of the surface, producing a loose layer, 

 furnishes the most favorable condition for the ready removal of the 

 SOU by water, the loose soil being readily carried away with the 

 surface run-off. This condition is most noticeable in old roadways 

 which have been lowered by erosion sometimes 15 to 20 feet, and the 

 vertical walls along the sides show httle effect from later rains. 

 The control of this type of erosion by terracing is a simple matter. 

 Any sort of growth completely covering the ground will prevent 

 the excessive removal of soil material. 



DAMAGE TO FLOOD PLAINS. 



In clearing slopes Inllside erosion is often so increased that the 

 streams carry a much larger burden of material than usual. The 

 excess material is deposited in the lower courses of the streams, 

 causing a filling or shifting of the channel. One result is that in 

 times of heavy run-off the stream channel is not sufficient to carry 

 the increased volume of water and overflows result. The flood plain 



