Geol.— Vol. I.] TURNER— ORIGIN OF YOSEMITE VALLEY. 305 



over the spur. The preservation of the patches of polish 

 seen on the western walls of the valley is due to their 

 being covered with soil or moss. 



The narrow, rugged canyon of the Merced to the west of 

 the valley, when seen after a rain, shows obscure traces of 

 groovings on the south wall, several hundred feet above the 

 river. Further west, we find no more groovings, or polish, 

 but several definite moraines give evidence that the ice 

 extended a little beyond Big Meadow. At Big Meadow there 

 are moraines of some size, at an altitude of from 4,500 to 

 5,200 feet; and on the south side of Merced Canyon, oppo- 

 site the Big Meadow moraines, are others something more 

 than 4,500 feet in elevation. On the spur down which 

 winds the trail which leads from McCauley's to the Merced 

 River, there are two small morainal patches, the lower one 

 of which has an altitude of 3,200 feet, the altitude of the 

 river being here only 2,100 feet. This moraine marks the 

 west limit of the great Merced glacier, so far as present 

 evidence goes. The ridge west of Little Crane Creek, to 

 the south of the Coulterville road, was examined for 

 morainal stuff, but none was found. The only objects sug- 

 gestive of the former presence of morainal material were 

 three well water-worn pebbles picked up on the ridge-top 

 and on its spurs, and these might easily have come from 

 former beds of Neocene River gravel, now completely 

 eroded. 



g. Ai'ea Covered by the Yoseniite Glacier. 



Having now presented evidence that there was a glacier 

 in Yosemite Valley, let us take a look at its extent or super- 

 ficial area. This glacier not only occupied all of the pres- 

 ent Merced drainage basin above the Yosemite, but received 

 important accessions from overflows of the much larger 

 Tuolumne glacier. Ice entered the valley from Yosemite 

 Creek, Tenaya Creek, Little Yosemite Valley, and possi- 

 bly Illilouette Creek. 



The largest tributary ice-mass without much doubt was 

 that of the Tenaya glacier. For, while the Tenaya Creek 

 drainage basin is small compared with that of the Merced 



