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FIRST TEAR SCIENCE 



stream increases very rapidly if its velocity is increased. 

 A stream having its velocity doubled will carry several 

 times as much material as before. Thus it happens that 

 water running over a surface sweeps loose material with 

 it, the amount varying with the rapidity and volume of 

 the flowing water. 



As this loose material sweeps over solid surfaces, it cuts 



GULLIES BEING CUT BY RUNNING WATER. 



them down. Thus flowing water is continually wearing 

 down and sweeping away the surface over which it moves. 

 This sort of work is called water erosion. 



When running water is. concentrated into a stream, the 

 work of erosion is also concentrated and the wearing down 

 of the stream bed becomes comparatively rapid. This 

 cutting down goes on irregularly, being greatest- at time 

 of flood and least when the flow is slight. It is estimated 

 that the solid material carried by the Mississippi River 



