300 CALIFORNIA ACADEMY OF SCIENCES. [Proc. 3D Ser. 



the lavas and gravels have been washed out by water and 

 gouged out by ice, and has probably been only slightly 

 deepened since the close of the Tertiary. The stream in 

 Deep Canyon has a very slight grade, so that there are fre- 

 quent stretches of nearly still water. 



A section drawn to scale (Plate XXXVI-yl), across Deep 

 Canyon and the Grand Canyon of the Tuolumne, illustrates 

 the relation of the Neocene and present surface at this 

 point. The dotted line is supposed to represent the old 

 Neocene surface. It exactly represents it at two points; 

 immediately where it intersects the contour of the present 

 surface south of Deep Canyon, and north of the Grand 

 Canyon. The ridge between Deep Canyon and the Grand 

 Canyon is capped with Tertiary lavas, beneath which the 

 old Neocene surface is still intact. 



Another interesting feature of this Tertiary river is that 

 it flowed over the present site of Hetch Hetchy Valley, 

 for the ridges both north and south, to the west of Deep 

 Canyon, are too high for it to have taken any other course. 

 The present canyon of the Tuolumne was thus in part ini- 

 tiated in Tertiary time. It is quite probable that this was 

 likewise true of the Merced canyon at Yosemite Valley. 

 It is quite certain that some of the marked benches along 

 the middle fork of the San Joaquin River are of Neocene 

 age for they are covered with Neocene lava flows. 



The chief evidence tending to show that there were two 

 glacial epochs consists in the existence of moraines on the 

 summits of ridges farther west than we are able to trace 

 evidences of glaciers in the canyons. This may be noted 

 in the canyon of the Middle Stanislaus, in the Big Trees 

 quadrangle (Plate XXXVI-C). The gentle contour of the 

 upper portion of this canyon at the point where the section 

 is drawn appears to represent a former shallow river valley. 

 On the ridges on either side are small moraines and boul- 

 ders which could easily have been left in their present 

 position if we suppose that during an earlier glacial epoch 

 this shallow valley was filled with ice. In this hypothetical 

 shallow canyon of an early date a rugged and deep 



