FORMER GLACIATIOX OF THE MERCED VALLEY. 45 



that the remarkable scenic features of that locality are, in some way, the 

 result of glacial action. It seems surprising that a theory so utterly averse 

 to the facts should have ever gained currency, and it is almost humiliating 

 to be obliged to enter into an argument to prove that the Yosemite Valley 

 was not dug out of the solid granite by ice. 



The head of the Merced hardly reaches the summit of the Sierra. It is 

 lapped around by branches of the San Joaquin on the south, and of the Tuo- 

 lumne on the north. All three of these streams head in the great central 

 mass of which Mount Maclure and Mount Lyell are the dominating peaks. 

 From this nodal point, however, great spurs extend to the southwest and 

 northwest, enclosing triangular areas between themselves and the main 

 divide, and which are drained by the tributaries of the San Joaquin and 

 Tuolumne, thus limiting the extent of the real summit range included in 

 the basin of the Merced to a distance of hardly more than a couple of miles 

 on the west side of the Mount Lyell Group. 



The real sources of the Merced are the various streams coming down from 

 the southwest side of the spur of the Sierra which leads from Mount Mac- 

 lure to Cathedral Peak, and from the northeast flanks of the Mount Clark 

 Range. The latter is a lofty mass of granitic rocks, which runs parallel with 

 the main crest of the Sierra, at about eight miles' distance, and is connected 

 with it by a transverse ridge. The plateau-like space thus enclo.sed is about 

 eight miles by ten in dimensions, wdth sides rapidly descending towards the 

 centre, where in a deep cailon runs the Merced. The lower portion of this 

 quadrangular area was formerly occupied by a glacier whose arms extended 

 up the depressions between the different spurs coming down from the main 

 ridges enclosing it on three sides. 



The glacier which was thus formed at the head of the Merced was probably 

 not by any means as thick, and it certainly was not so extensive, as that 

 which occupied the Upper Tuolumne Valley on the other side of the Cathe- 

 dral Peak Range. The reasons of these inferior dimensions are easily found 

 in the smaller size and diminished altitude of the iratherino;-o;round at the 

 head of the Merced. This latter is nearly tAvo thousand feet lower, on the 

 average, than the broad valley to the north, which formed the main reservoir 

 into which descended the numei-ous tributaries which combined to form the 

 main glacier of the Tuolumne. The area at the head of the Merced, besides 

 having the disadvantage of inferior altitude, is so situated that it could 

 receive only one important tributary, namely, that coming down on the east 



