CHAPTER XXI 

 EROSION AND SEDIMENTATION 



236. Removal of the soil : erosion. When the formation of 

 soils was being discussed, we spoke of the action of water 

 upon rocks, gravel, and sand. We have but to look at a large 



FIG. 104. Erosion by a stream 



A swiftly flowing stream wears down its bed rapidly and forms a steep-walled 

 valley. (Tumwater Canon, Washington.) Photograph by W. B. MacCallum 



river (fig. 104) or a gutter stream to get an idea of the power 

 of water to carry soils. A study of a surface stream that is 

 flowing from a field or garden will tell a good many things 

 about erosion. First, the heaviest particles of soil that are 

 moved are carried only by the strongest part of the current. 



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