THE WORK OF RUNNING WATER. 



137 



One waterfall often breeds others. Thus where a fall recedes 

 beyond the mouth of a tributary stream, the tributary falls. The 

 Falls of Minnehaha, on a small tributary to the Mississippi, near Min= 

 neapolis, may serve as an illustration. In such cases the falls may 

 not develop from rapids. Once in existence, the fall of a tributary 

 follows the same history as that of a main stream. 



Streams which have falls are relatively clear. ^ If a stream favor- 



FiG. 117. — Kepler's Cascade, in the Yellowstone Park. The jointed and fractured 

 character of the igneous rocks occasions a series of falls and rapids. (Iddings, 

 U. S. Geol. Surv.) 



ably situated for the development of a fall carried a heavy load, de- 

 position would take place below the rapid s, and the tendency would 



1 Gilbert. Am. Jour. Sci., Vol. XII. p. 99, 1876. 



