THE WORK OF RUNNING WATER. 



IS.'j 



these conditions, as well as the rapids preceding and following, would 

 remain constant in position until the resistant layer was brought to 

 grade, but the}^ would ultimately disappear as in the preceding cases. 

 Falls are not hkely to develop where the strata of the stream's bed dip 

 down-stream, though they may develop even under these conditions if 

 the gradient of the stream is greater than the dip of the strata (Fig. 116). 



Fig. 114.— Falls in Utica shale, Canajoharie, N. Y. (Darton, U. S. Geol. Surv.) 



The inequality of resistance in the rock which occasions a fall 

 may be original or secondary. In the case of Niagara Falls ^ (Fig. 113) 

 relatively resistant limestone overhes relatively weak shale. At the 

 Falls of St. Anthony (Minneapohs) limestone overlies friable sandstone. 

 The falls of the Yellowstone and the Shoshone Falls of the Snake River 

 (Idaho), are in igneous rock. In the former case the unequal 



^ Gilbert, article on Niagara Falls, in Physiography of the United States. 



