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Show EECENCY 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 excavated 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 incessant grinding of its turbid waters 3,000 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 extent 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 surface 6,000 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 buttes 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 insufficient to sensibly modify |
