THE WORK OF RUNNING WATER. 



193 



level. Even small creeks at high altitudes may meander, if so situated 

 as to have slight velocity. Trout Creek in the Yellowstone Park (Fig. 

 184) is an example. 



There seems to be some relation between the width of the belt 

 within which a stream meanders, and the width of the stream itself. 

 Recently io has been estimated 

 that the ratio between them is 

 18:1.^ 



During the development of the 

 meanders it is to be noted that 

 lateral planation on the one side of 

 a stream is accompanied by deposi- 

 tion on the other. This is cut- 

 and-fill. The sediment eroded 

 from the curve which is concave 

 toward the stream is shifted down- 

 stream, while that deposited in the 

 curve which is convex toward the 

 stream is brought down from 

 above. Thus even in the develop- 

 ment of meanders, the material 

 which is dislodged is shifted down- 

 stream. Since the current directed ^^^- l^S.-Bayou Lakes Osage River, near 



Butler, Mo. 



against the down-stream side of a 



growing meander is on the average stronger than that directed against 

 the opposite side, the meander itself has a tendency to migrate down- 

 stream (Fig. 182). 



In their evolution, the curves of a stream's channel often reach 

 and undermine the valley bluff (PL VII). Since the meanders are, 

 on the average, shifted down-stream individually, and since meanders 

 are frequently developed in new places, it follows that a meandering 

 stream tends to widen its valley throughout. Widening is also effected 

 in other ways, for a stream with a flood-plain sometimes abandons 

 its channel altogether for miles at a stretch, and the new course chosen 

 may be against one of the bluffs of the valley. Such changes are most 

 likely to take place where deposition along channel and levees has 



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