14 



Sierra Club Bulletin. 



On its up-stream side the ridge is buried under lake deposits, 

 and only the upper fifteen feet emerge. On its down-stream 

 side it slopes down twenty-five to thirty feet, but here, too, its 

 foot is covered by river gravels of unknown depth. Examina- 

 tion of other moraines in the Yosemite region, more especially 

 those of the later ice invasions, to which the El Capitan moraine 

 itself belongs, seems to indicate, however, that a height of one 

 hundred feet is the maximum assignable. The majority of these 

 ridges scarcely exceed fifty or sixty feet in height. Five- 

 hundred-foot moraines are foreign to the region. 



If the El Capitan moraine is not over one hundred feet high, 

 how, then, shall we account for the great depth of Lake Yo- 

 semite, as indicated by the diagram? The answer is, by assum- 

 ing the existence of a deep basin eroded in the rock floor of 

 the valley by the ice. There is nothing violent in that assump- 

 tion. Glaciers normally excavate extensive rock basins in the 

 bottoms of their valleys. The well-attested instances of such 

 action are literally numberless. Lake basins are a familiar 

 feature of all glaciated mountain regions, and in some cases — 

 such as that of Lake Chelan — they occur on a truly stupendous 

 scale, dwarfing Lake Yosemite into insignificance.* 



Nor need one go outside the Yosemite region for examples. 

 There is evidence of a lake basin on every tread of the stair- 

 wise descending branch canons. The stair-Hke character of 

 the floors of these cations, it may be pointed out in passing, is a 

 distinctly glacial trait, and the presence of lake basins hollowed 

 out in the treads is only one of the concomitant features. 



Thus the entire Little Yosemite Valley was once occupied by 

 a lake. Filled with river gravels, like the main valley itself, it 

 now presents the appearance of a gradeless fiat of some three 

 miles, above which only the crests of several curving terminal 

 moraines emerge. 



On the tread immediately above the Vernal Falls, again, is 

 Emerald Pool, diminutive, yet as typical a glacial rock basin as 



* The writer's attention has been called to what appears to be rock-in-place visible 

 in the bed of the Merced in the upper part of the valley. The supposed great 

 depth of sedimentary filling in the valley would thereby seem to be discredited. A 

 visit to the spot in the fall of 1910, however, enabled the writer to satisfy himself 

 that the outcrop of rock reported is in reality only an indurated bed of coarse river 

 sand, irregularly gullied out by the current, and closely resembling solid granite. 

 It is friable in the hand and is underlain by unconsolidated layers of sand and silt. 



