RECENCY OF FAULTS. 37 



were severed from the platforms below Realizing how slowly to human 

 senses these processes operate, the thought of the long ages through which 

 they have been at work at first oppresses us, and we are conscious only of 

 a duration which we can no more comprehend than we can comprehend 

 eternity. Yet, when we come to compare the work which has been done 

 upon the flanks of the plateaus with what we are sure has been done upon 

 the regions they overlook, the former sinks into insignificance. 



Since the commencement of the faulting ravines have been exca- 

 vated 2,000 or 3,000 feet in depth ; some of the living streams have sunk 

 their canons from a few hundred to a thousand feet ; here and there a patch 

 of exposed country has lost some hundreds of feet of strata ; old volcanic 

 vents on which possibly stood cones have moldered away and left barely 

 a heap of unintelligible ruins. More than this: we know that since the 

 same epoch the inner gorge of the Grand Canon has sunk under the inces- 

 sant grinding of its turbid waters 8,000 feet into the earth, and its side gorges 

 near the river have deepened an equal amount. Doubtless many other 

 changes have occurred, the precise nature and exteni of which we can only 

 conjecture. Such as we recognize seem stupendous to us and even stagger 

 us when we look at the instrumentality to which we must attribute them. 

 But these are only the last touches of the work which has denuded an 

 empire, sweeping from its surfiice fi, 000 feet of strata. 



When we study more closely the later erosion, we find that by far the 

 greater part of its results are of that class which is effected with the greatest 

 ease and rapidity. Slow as the process seems to our senses which has cut 

 gorges and canons, it is swift and trenchant when compared with the 

 moldering of cliffs and the decay of butte's and mesas ; and this slow decay 

 is far less slow than the decay of platforms and terrace summits. It is in 

 ravines and canons that the denuding forces work to the utmost advantage. 

 Let a plateau or mountain range arise, and the streams will dissect it to its 

 core before it will have materially suffered otherwise. Such uplifts as we 

 find in the Plateau Province have given to the streams which flow from 

 them the most favorable opportunity to corrade, and they have cut profound 

 gorges ; but the amount of waste upon the summits and even upon the 

 great palisades which bound them has been insufiicient to sensibly modify 



b 



