SOIL EROSION IN THE SOUTH. 5 
near its confluence with the Mississippi, 176,000,000 tons, with cor- 
responding amounts carried by various other rivers. Enormous as 
these figures are, they do not represent by any means the total losses 
from the soils drained by the streams. No estimates of the total 
amount of material actually moved through the agency of water 
has been made, but it must be many times greater than the amount 
which reaches the sea in suspension. 
A case is reported by Tarr * describing the intense action of a flood 
in an arroyo in the Rio Grande Valley, New Mexico, due to a local 
cloudburst in the Donna Ana Mountains of about half an hour dura- 
tion and extending over an area of less than 6 square miles. Such 
large quantities of material were brought down from the hills that 
several acres were covered with silt and gravel. An adobe house 
about 10 feet high was buried to within 2 feet of the top. Several 
thousand tons of earth must have been transported during this 
sudden rush of water. Tolman 2 describes the transporting of 
material by streams of the arid region. The quantities of sand being 
carried to the sea are discussed by Marsh. 3 In addition to the solid 
particles carried to the sea by the streams, the quantity of dissolved 
material is also enormous. It is estimated that the Mississippi 
River carries annually to the Gulf of Mexico 86 tons of dissolved 
salts from every square mile drained by it. The rivers of the West 
carry much larger quantities than this. 
MOVEMENT OF SOIL MATERIAL BY THE WIND. 
The total amount of soil material moved by water is large, a fact 
well known, but the fact that almost equally as large amounts are 
moved through the agency of the wind is not generally appreciated. 
The wind exerts its action in any direction or in any climate. While 
it is true that the greatest effect is shown in arid or semiarid regions, 
the wind of the humid regions always carries a burden of suspended 
soil material. The dry material of an arid climate is more easily 
moved, and hence the greater effect produced. 
In considering the transporting capacity of wind, Free 4 has esti- 
mated from experiments by Udden 5 that the capacity of winds 
blowing over the Mississippi basin is probably at least a thousand 
times as great as the transporting capacity of the river. The wind, 
however, is usually loaded to only a small fraction of its capacity, 
so that the amount of material transported is very much less than 
its capacity. It is certain that the quantities actually moved by 
the wind are very large, and this movement contributes much to 
the change of soil surface conditions. 
i Tarr, Am. Naturalist, 24, 456 (1890). 
2 Tolman, Jour. Geol., 17, 142 (1909). 
a Marsh, The Earth as modified by Human Action, Ed. 1888, p. 528. 
« E. E. Free, Bureau of Soils Bull. No. 68, p. 46 (1911). 
& Jour. Geol., 2, 326(1894). 
