FORMATION OF THE YOSEMITE VALLEY. 49 



former extension of the glaciers over the higher portions of the Sierra, a few 

 words may be added to wliat has been said, for the purpose of showing that, 

 even had the Valley been so occupied, there is no reason to believe that its 

 form would have been essentially modified by any erosive agency of the ice 

 which passed through it. Bearing in mind what has already been said in 

 regard to the glaciation of the Tuolumne Canon and the Hetch-Hetchy 

 Valley, it may be added that the form of the Yosemite is still more unlike 

 anything that could have been effected by any kind of ero.sive action, 

 whether of ice or water. Following down the Merced from the Little Yo- 

 semite, we have in tiie first place two vertical steps of descent, of 600 and 

 400 feet. Even now, after the river has poured its volume of water over these 

 precipices for ages, their edges remain wonderfully sharp. These vertical 

 steps downwards along the line of descent of the supposed glacial mass are 

 something of an entirely difterent natui'e from any results which either ice 

 or water is accomplishing at the present day. But the whole Yosemite shows 

 in all its details a succession of forms which never could have been produced 

 by any kind of erosion. Such rectangular, squarely cut recesses as that at 

 the head of the Valley, over which the Vernal and Illilouette falls descend, 

 could never have been produced by flowing material of any kind. And 

 all through the Yosemite there are vertical, or nearly vertical, walls of rock 

 from one to two thousand feet in height, which are turned entirely in the 

 opposite direction, and, so to speak, hidden away from any possible approach 

 of an erosive agent. An examination of the large map of the Valley accom- 

 panying the 8vo and 4to editions of the Guide-Book would suffice to con- 

 vince any candid inquirer that such faces of rock as those on the west side 

 of El Capitan differ I'adically from anything exhibited by oi'dinary valleys of 

 ei'osion. A moving mass of ice could only have acted in the direction of its 

 own line of motion. Angular forms could never by any possibility be cut 

 out at right angles to that direction. Most surprising, and contrary to all 

 the facts, is the attempt which has been made to explain such remarkably 

 exceptional formations as that of the Half Dome by glacial erosion. The sum- 

 mit of this stupendous mass rises to a height of more than 2,000 feet above 

 any point which ice could ever have reached. It has not a glacial scratch 

 upon its surface at any point. Its smoothly rounded back and dome-shaped 

 summit are found on examination to be strictly conditioned b}- the internal 

 structure of the mass itself, which along the edges of its broken front everj'-- 

 where shows the overlapping concentric shells of which it is made up. As 



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