3l6 CALIFORNIA ACADEMY OF SCIENCES. [Proc. ^d Ser. 



suggested, in virtue of which the rock-mass out of which 

 the gorge is cut was differentially elevated. No evidence of 

 such faulting was found, and although faulting in massive 

 rocks, such as the granites of Yosemite Valley, is not so 

 easily made ovit as with bedded rocks, yet if such faulting 

 is at all extensive, the granite can not fail to be sheared 

 and cataclastic or crushed structure more or less perfectly 

 developed. 



Hetch Hetchy Valley on the Tuolumne River is com- 

 monly spoken of as a smaller Yosemite. Like the latter, 

 the river west of it flows through a narrow gorge. This is 

 in places but thirty or forty feet wide, and this outlet is in- 

 sufficient for the outflow of the water at the time of the 

 melting of the snows in the spring, so that even now the 

 lower end of the valley is a lake for part of the year. 

 There is, beyond all question, a zone of faulting across 

 this gorge at its mouth. The rocks are granites and 

 gneisses and are thoroughly crushed and broken along the 

 larger faults. Specimens of the rock from one of these 

 faults show cataclastic structure under the microscope most 

 admirably. Moreover, in Hetch Hetchy Valley there is 

 no morainal material at its western end, at least not in suffi- 

 cient amount to dam up the valley. We may therefore con- 

 clude that the differential elevation of the west wall of 

 Hetch Hetchy may have formed a rock barrier which 

 dammed back the water and eventually resulted in the de- 

 posit of the sediment of the valley floor. By this it is not 

 meant to imply that the canyon itself was the result of 

 faulting. The Tuolumne canyon like the Merced was 

 doubtless cut out chiefly by water, and afterward cleaned 

 out by a glacier which has left strong groovings at many 

 places on the walls. This glacier filled the valley and ex- 

 tended several miles farther west down the canyon. 



/^. Conclusions. 



The following theories have been advanced to account 

 for the formation of Yosemite Valley: — 

 I. That it was scooped out by ice. Muir. 



