1883.] on the Cations of the Far West. 271 



have occurred across tlie pathway of the river, but without in any way 

 deflecting it. 



The influence of subterranean movements is shown in successive 

 terraces with intervening platforms, as in other rivers. The terraces, 

 however, do not consist of alluvium but of escarpments of solid rock. 



In forecasting the future history of the canons, we find that the 

 Grand Canon has somewhere about 1000 feet to remove from the 

 bottom of its channel before its slope becomes so slight that its 

 erosive power will nearly cease. It is conceivable that should no 

 geological revolution occur in the region, the caiion may be still 

 deepened to that amount. There are indications, however, that a 

 limit may be set to the possible depth of the chasm. Like the creej) of 

 a coal mine, where the floor is squeezed upwards by the pressure of 

 the enormous superincumbent weight on either side, the bottom of 

 the caiion, relieved from the weight of the overlying column of rock, 

 may be forced upwards by the pressure of the walls on either side. 

 In that case, the channel might rise as fast as the river cut it down, 

 so long as nothing occurred at the surface to materially diminish the 

 height of the walls. 



[A. G.] 



Vol. X. (No 76.) 



T 



