CHAPTER IV 

 THE WORK OF RUNNING WATER 



Streams are of common occurrence in most lands. A few, like 

 the Mississippi and the Amazon, are very large, but small ones are 

 far more numerous. Some are sluggish, and some swift. Even 

 those which flow slowly under ordinary conditions may become 

 swift in times of flood, and then their force may be terrible (Fig. 

 37) . Occasionally they sweep away bridges, dams, and even build- 

 ings which stand upon their banks. The strong beams and rods 

 of the bridges, and the steel rails of railways, are in some cases 

 bent as if they were twigs by the force of the flood which follows an 



Fig. 37. A raging river. Flood of the Mississippi River breaking through 

 its levees. Louisiana. (U. S. Weather Bureau.) 



exceptional rain, or the rapid melting of a large body of snow. 

 The destruction or the weakening of bridges by flooded streams 

 is a common cause of railway accidents. The force of a stream is 

 no less where there are no bridges or buildings, and its banks and 

 bed are effectively worn by the swift current. 



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