SOIL EROSION" IN" THE SOUTH. 5 



near its confluence with the Alississippi, 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 ^ describes the transporting of 

 material by streams of the arid region. The quantities of sand being 

 carried to the sea are discussed by Marsh.'' 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 Llississippi 

 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 vnnd 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 



[U- soil material. The dry material of an arid climate is more easily 



P moved, and hence the greater effect produced. 



In considering the transporting capacity of wind, Free * has esti- 

 mated from experiments by Udden ^ that the capacity of winds 

 blowing over the Mssissippi basin is probably at least a thousand 



I 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 mucli less than 

 its capacity. It is certain that the quantities actually moved by 

 the wind arc very large, and tliis movement contributes nmch to 

 the change of soil surface conditions. 

 I > TaiT, Am. NaturalLst, 24, 456 (1890). 



I »Tolnian, Jour. G(y)l.,^l7, H2 (IWW;. 



I » .Marsh, Tho Karth an'modlfled hy Human Action, Ed. 1888, p. 528. 



* < K. K. iTM, Huntau of HolLs Hull. No. 08, p. 40 (1911), 



<■ Jour. Qwil., 2, 326 (1894). 



