AQUEOUS AGENCIES. 29 



cutting again and form deep cafLons. These deep canons 

 are therefore characteristic of new topography i. e., of a 

 rising or newly risen land and of rivers far above their 

 base-level and working hard to reach it. If on the other 

 hand the land sinks, the rivers become more sluggish 

 they cease to cut and begin to build up by deposit. Thus 

 river channels become delicate indicators of the move- 

 ments of the earth's crust. 



2. Winding Course of Rivers. 



The winding course of rivers is the necessary result of 

 the laws of currents. Streams do not find irregular chan- 

 nels to which they are forced to conform, but they make 

 their own channels. If we straighten these channels, 

 they will not remain straight. Some point will wear into 

 a hollow. This will throw the stream to the other side, 

 which will in like manner be worn, and thus the stream 

 begins to meander. Now, if we examine any winding 

 stream, we shall see that the swiftest current is on the 

 outer part of the curve and the slowest on the inner side, 

 or, in other words, the current is swifter than the aver- 

 age on the outer and slower than the average on the inner 

 side of the bends. In the figure, the arrows show the 



FIG. 8. 



line of swiftest current. Now, if the river is carrying 

 all the sediment its average velocity can, it is evident that 

 it will cut on its outer curve, where the velocity is greater 

 than the average, and deposit and make land on the 

 inner side, where the velocity is less than the average. 

 Thus the outer curve is increased by erosion and the 



