74 BACTERIA AND SOIL FERTILITY 



sands. The eifectiveness of the sand blast is recognized in the 

 industries where it is often used for the grinding of hard surfaces. 



Wind plays a tremendous part in the transporting of soils. 

 Emerson states, "Dust storms are not uncommon even in humid 

 regions, and a strong wind may in a few hours carry away one 

 one-hundredth of an inch of soil. At this rate it would require 

 only one hundred winds to move one inch of loose material and 

 only 1,200 winds to move a foot, a rate that, from a geological 

 point of view, is comparatively rapid." It has been estimated 

 that the transporting power of winds over the Mississippi Basin 

 is about one thousand times as great as the transporting powers of 

 the Mississippi itself. Moreover, it is stated that every square 

 mile of the earth's surface contains soil from every other square 

 mile carried to it by the atmosphere. 



There have been times in Colorado when sanddrifts a foot 

 high have been piled on a railroad track in half an hour, thirteen 

 carloads of sand being removed from a single platform on one 

 occasion. The soils of the famous palouse wheat regions of 

 eastern Washington, eastern Oregon, and northern Idaho were 

 probably formed in just this manner. 



Running Water. — ^The transporting and erosive power of 

 water is apparent to all who have looked into a stream. One 

 can see at almost any time grains of sand and rocks of various 

 sizes, rolling, hopping, sliding, along the bottom of the stream. 

 These grind against one another and against rocks in the beds 

 and banks of the streams, slowly but continuously scouring out 

 its bed and reducing the rocks to finer particles. The speed with 

 which this result is accomplished varies with the volume and 

 speed of the current. If a stream's velocity is doubled the 

 carrying power is increased sixty- four times. With this in mind, 

 one can understand how a stream in flood can transport even 

 large bowlders. Thus, all streams are continuously transporting 

 sand, rock, or soil from the higher to the lower levels. A nat- 

 ural barrier may impede the flow of the stream, then it stops to 

 "pause for a sleep and dream." But after this sleep, how it romps 

 and plays in the gathering of another load! 



