SOIL-FORMING PROCESSES 15 



The water, in order to be a successful cutting agent, must 

 be laden with sediment, so that its carrying power largely 

 determines its power of erosion. In other words, it must 

 be armed. 



From the time when the raindrops beat down on a 

 surface until they have been gathered into rivulets and 

 streams and finally discharged into the ocean, they are 

 engaged in moving the detrital matter already produced. 

 The Mississippi River is working fast enough at the 

 present time to reduce the continent of North America 

 to sea level in four million years. The Appalachian 

 Mountains, born in Paleozoic times, have lost vastly 

 more material than now remains for us to view. Our 

 river and lake soils are due to the cutting and carrying 

 power of the streams. The deltas, and the marine soils 

 of the Atlantic and Gulf coasts, afford other examples 

 of such effects. The continual pounding and grinding 

 of waves are no mean factor in rock disintegration. The 

 rounding of the sands is a mute evidence of this great 

 force. 



11. Wind. — The wind as a soil-forming agent has, 

 like water, two phases of action — erosive and transpor- 

 tive. Sweeping over the land in dry weather, it has the 

 power of picking up innumerable fine particles which 

 may abrade rocks very noticeably over a term of years. 

 The fluting of exposed rocks, especially in arid regions, 

 the undermining of cliffs, and the polishing of stones 

 to a smoothness equal to that of glass, are frequent occur- 

 rences. The roughening of windowpanes in houses near 

 the seashore during severe storms, and the illegibility 

 of old tombstones, are of common record. Great areas 

 of soil have been deposited by winds, especially in the 

 United States. The loess of the Mississippi Valley and 



