302 E. C. ANDREWS. 



valley sides was thus formed at the conflence of the Tenaya 

 and Merced Glaciers. The comparatively weak Illilouette 

 was undercut and hung well up over the Merced Valley. 

 A still more pronounced canon constriction or "narrow " 

 occurred at El Capitan. Just in front of this and the 

 Cathedral Spires a basin was formed. This basin was then 

 carried upstream by headward recession along a gently 

 rising grade. During the recessional movement lateral 

 action with great sapping between the 6,000 and 7,000 feet 

 levels was very pronounced, especially in the more decided 

 "narrows" and along the cutting curves. The associated 

 forms of El Oapitan, the Cathedral Spires, and Bridal Veil 

 Falls, originated in the relatively rapid motion of the glacier 

 caused by the canon contraction at this point. Glacier 

 Point and Yosemite Falls faced either resultant or reflected 

 ice thrusts and they thus formed cutting curves. The 

 whole valley may be considered as a pronounced canon 

 constriction, but contraction of the valley walls is more 

 accentuated in some places than in others. Both the 

 Yosemite and Bridal Veil Falls are splendid examples of 

 the removal of the lower portions of weak tributary 

 channels possessing high grades. 



As the basin which was formed at Inspiration Point and 

 El Capitan grew by headward recession until it was con- 

 nected with the basin or flat formed at the Tenaya and 

 Merced junction, the latter basin also retreated along the 

 steep declivities of both these tributaries. The steep 

 channel slopes possessed at this stage by the lower Tenaya 

 and Merced gave their glaciers wonderfully increased 

 power locally. Thus each ice stream commenced heavy 

 quarrying operations. Strong structural planes were made 

 use of, and an immense V-shaped notch was made in the 

 Tenaya Channel, and the two steps of the Nevada and 

 Vernal Falls in the case of the Merced. The time factor, 



