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Sierra Club Bulletin 



lakes, often halting with an embarrassed air and turning back, 

 groping their way as best they can, moving most Hghtly just 

 where the glaciers bore down most heavily. With glaciers as a 

 key the secrets of every valley are unlocked. Streams of ice 

 explain all the phenomena; streams of water do not explain 

 any ; neither do subsidences, fissures, or pressure pUcations. 



We have shown in the previous pa-ptrthdit post-glacial streams 

 have not eroded the 500,000th part of the upperMerced canons. 

 The deepest water gorges with which we are acquainted are be- 

 tween the upper and lower Yosemite falls, and in the Tenaya 

 Canon about four miles above Mirror Lake. These are from 

 twenty to a hundred feet deep, and are easily distinguished 

 from ice-eroded gorges by their narrowness and the ruggedness 

 of their washed and pot-holed sides. 



The gorge of Niagara River, below the falls, is perhaps the 

 grandest known example of a valley eroded by water in com- 

 pact rock ; yet, comparing equal lengths, the glacier-eroded val- 

 ley of Yosemite is a hundred times as large, reckoning the aver- 

 age width of the former 900 feet, and depth 200. But the ero- 

 sion of Yosemite Valley, besides being a hundred times greater, 

 was accomplished in hard granite, while the Niagara was in 

 shales and limestones. Moreover, Niagara cafion, as it now ex- 

 ists, expresses nearly the whole amount of erosion effected by 

 the river ; but the present Yosemite is by no means an adequate 

 expression of the whole quantity of glacial erosion effected 

 there since the beginning of the glacial epoch, or even from 

 that point in the period when its principal features began to be 

 developed, because the walls were being cut down on the top 

 simultaneously with the deepening of its bottom. We may fair- 

 ly ascribe the formation of the Niagara gorge to its river, be- 

 cause we find it at the upper end engaged in the work of its fur- 

 ther extension toward Lake Erie ; and for the same reason we 

 may regard glaciers as the workmen that excavated Yosemite, 

 for at the heads of some of its branches we find small glaciers 

 engaged in the same kind of excavation. Merced canons may 

 be compared to mortises in the ends of which we still find the 

 chisels that cut them, though now rusted and worn out. If Ni- 

 agara River should vanish, or be represented only by a small 

 brook, the evidence of the erosion of its gorge would still re- 



