6 BULLETIN 180, U. S. DEPARTMENT OE AGRICULTURE. 
EXCESSIVE TRANSLOCATION OF SOIL MATERIAL. 
The methods of translocating soil material either by wind or water 
have played important parts in the geologic history of the earth. 
The complex relations between topography, climate and erosion, 
and transportation and sedimentation can not be discussed in a paper 
of this character, but these relations are clearly brought out in articles 
by Joseph Barrell. 1 
It is uot with this movement of material in its natural condition 
that we are especially concerned, but with conditions in which man 
has for some purpose, either for agriculture, lumbering, mining, or 
power, interfered with the natural process, so that an excessive 
removal of soil material results. Since it is necessary to follow the 
vocations that disturb the balance established by nature between 
rainfall, slope, and erosion, methods of minimizing this disturbance 
as much as possible should be determined and employed. 
CAUSES OF EROSION. 
Erosion of land surface is produced by water flowing over its surface 
or by wind action. Wind erosion has been studied and described by 
Free and the general principles underlying soil erosion by water have 
been described by McGee, 2 so that only a short statement is here 
necessary. In the South it is of course the action of water that plays 
the more important part in soil translocation. 
Water reaching the surface of the soil either sinks into the soil, 
evaporates, or runs off the surface. That portion which evaporates 
enters into the formation of clouds and is later returned to the earth; 
the portion that sinks into the ground increases the underground 
store of water, a part of it reaching the streams and wells by seepage 
and a part being returned through capillary action to the surface, 
where it may be utilized in the growth of plants, or may join the 
evaporated portion. This downward movement into the soil causes 
a slight movement of particles, resulting in the alteration of the 
mechanical composition of the soils and subsoils, 3 but this is small 
in comparison to the movement of soil material by the water which 
runs off the surface. It is this water which lifts and carries along 
soil material, cutting into the soil surface and leaving it bare and 
gullied. 
The water running off the surface of the soil has been estimated in 
a number of cases. The Illinois experiment station 4 reports that 
48.9 per cent of the rain falling in the Savannah Kiver basin reaches 
the sea. Of the rain falling in the Potomac drainage basin it is esti- 
i Jour. Geol., 16, 159, 255 and 363 (1908). 
2 W J McGee, Soil Erosion, Bui. Xo. 71, Bu. of Soils, U. S. Dept. of Agr. (1911). 
s Davis and Fletcher; Distribution of Silt and Clay Particles in Soils. 8th Internat. Cong, of App. Chem. , 
15, 81 (1912). 
* HI. Expt. Sta. Circ. Xo. 119 (1908). 
