2 BULLETIN 512, U. S. DEPARTMENT OF AGRICULTURE. 
matter per acre of land drained, containing plant food sufficient to 
produce a crop. Unless this loss be replaced by natural agencies or 
by the application of fertilizer, it is obvious that the land soon will 
deteriorate greatly in productiveness and eventually be abandoned. 
In addition to the loss of the soluble elements of the soil, a notice- 
able impairment occurs in the physical condition of the soil. When 
the moving water washes the soil particles from the surface of the 
hillside and deposits them on the land below, the heavier particles, or 
the sandy constituents of the soil, are deposited first, and the finer, or 
clay, parts last. Since neither pure sand nor pure clay possesses the 
productive characteristics observed in a soil composed of the proper 
intermixture of sand and clay particles, it is apparent that the 
effect of this sorting process is to diminish greatly the fertility or 
productive power of the soil. Hence, not only the eroded land suffers 
but also the land at a lower level upon which the eroded material is 
deposited. Portions of the flood plains of small streams often are 
covered with a layer of sand, the fertility of the land so covered be- 
ing practically destroyed, since it is a most difficult task again to 
build up a productive soil over such areas. Drainage channels, also, 
constructed at considerable cost, often become filled with soil 
washed from the hill lands. (See Pl. I, fig. 1.) Asa result the ad- 
joining bottom land reverts to swamp ol becomes mapesuee for 
cultivation. 
FORMS OF EROSION.1 
Erosion due to moving water occurs in two forms—sheet washing 
and gullying. Small areas are practically ruined by gullying (PI. I, 
fig. 2), while sheet washing (PI. IJ, fig. 1) diminishes the produc- 
tive power of large areas. 
Gullying generally is the most dreaded of the two types on account 
of its more apparent destructive effects. Where the ravages of ero- 
sion proceed unchecked, deep gullies invariably develop in the field. 
Their appearance causes not only absolute loss of land and incon- 
venience in cultivating, but a marked lowering in the water table, 
with a possible accompanying inability of the soil to retain the 
proper moisture content for the production of crops and to withstand 
periods of drought. 
The injury due to sheet washing, which occurs throughout the 
United States, generally is underestimated and is regarded by many 
farmers as of no particular consequence. It is this type of erosion 
that slowly carries away the very fertility of the soil without appris- 
ing the farmer—except through slightly diminished crop yields each 
year—that the application of remedial measures is imperative in 
order to save his farm. To the very slowness of its action can be 
1For a more extended discussion of the translocation of soils, see U. S. Dept. Agr. Bul. 
180, by R. O. E. Davis. 
