Geol.— Vol. I.] TURNER-ORIGIN OF YOSEMITE i' ALLEY. 311 



but this is not the system which has determined the cHff at 

 the falls. The joints along which this cHff has formed are 

 part of the system which is well developed in the granite 

 just above the falls by the httle bridge over Yosemite 

 Creek. 



An inspection of the topographic map constructed by the 

 United States Geological Survey brings out the fact that the 

 cliff forming the north face of Half Dome and that east of 

 Illilouette Creek, just below the falls of the same name, 

 have the same trend. The shoulder west of Half Dome 

 shows vertical sheeting apparently parallel to the vertical 

 face of the dome. The Illilouette cliff as seen from the 

 Nevada Falls trail is plainly sheeted or jointed, the joints 

 dipping north at an angle of about 80°. The amphitheater 

 just below Illilouette Falls appears clearly to have been 

 formed by river erosion along this sheeted zone in the gran- 

 ite and presents an extraordinary similarity to the amphi- 

 theater at Fall River Falls, in Butte County, California, 

 which has quite certainly resulted from river erosion, since 

 the locality is far below the glaciated region. The escarp- 

 ment is here primarily due to the vertical sheeting of the 

 granite at the falls. A view of the Fall River amphitheater 

 is given in the Bidwell Bar Folio of the U. S. Geological 

 Survey. 



Inclined yoints. — Joints dipping at angles varying from 

 25° to 50° are not nearly so abundant as "the system just 

 described. They are, however, noticeably developed at 

 three points: Bridal Veil Falls, the Three Brothers, and 

 east of Glacier Point. Those at Bridal Veil Falls seem to 

 have been the cause of the V-shape of the ravine of Bridal 

 Veil Creek just above the falls, there being two sets of in- 

 clined partings, one dipping west and the other east. At 

 the Three Brothers a westerly dipping system only is 

 strongly developed. This is represented on Plate XXXIII, 

 which is a reproduction of a photograph by Fiske. Noth- 

 ing can be more evident than that the angular outlines of 

 the Three Brothers are primarily due to these inclined 

 joints. The slope of the spur extending east from Glacier 



