564 CENOZOIC ERA— AGE OF MAMMALS. 



favored by proximity to the sea, had their perpetual snow-cap from 

 which issued glaciers filling the principal valleys.* 



It is impossible to describe all the great ancient glaciers whose 

 tracks have been traced. They filled all the larger canons, and their 

 tributaries all the higher and smaller valleys and meadows. Their 

 tracks are everywhere marked by glaciation and strewed bowlders, and 

 their terminus at different times by a succession of terminal moraines 

 and lakelets. We will mention three or four as examples : 



a. During the epoch spoken of, a great glacier, receiving tributaries 

 from Mount Hoffman, Cathedral Peaks, Mount Lyell, and Mount Clark 

 groups filled Yosemite Valley, and passed down Merced Canon. The 

 evidences are clear everywhere, but especially in the upper valleys, 

 where the ice-action lingered longest. 



b. At the same time tributaries from Mount Dana, Mono Pass, and 

 Mount Lyell, met at the Tuolumne meadows to form an immense 

 glacier, which, overflowing its bounds a little below Soda Springs, sent 

 a branch down the Tenaya Canon to join the Yosemite glacier, while 

 the main current flowed on down the Tuolumne Canon and through 

 Hetchhetchy Valley. Knobs of granite, 500 to 800 feet high, standing 

 in its pathway, were enveloped and swept over, and are now left round, 

 and polished, and scored, in the most perfect manner. This glacier 

 was at least forty miles long and 1,000 feet thick at Soda Spring for its 

 stranded lateral moraine may be traced so high along the slopes of the 

 bounding mountain, and 2,500 thick farther down, for it filled Hetch- 

 hetchy Valley to the brim. 



c. The Sierra range on its western side slopes gradually for fifty or 

 sixty miles ; but on the eastern side it is very precipitous, so that the 

 plains 5,000 to 7,000 feet below the crest are reached in four or five 

 miles. In glacial times long and complicated glaciers with many tribu- 

 taries occupied the western slope, while on the eastern slope innumer- 

 able short, simple glaciers flowed in parallel streams down the steep in- 

 cline and out for several miles on the level plain, or even into the waters 

 of Lake Mono. One of the largest of these took its rise in the snow- 

 fields about Mono Pass, flowed down Bloody Canon, and six to seven 

 miles out on the plain, and evidently into the waters of Lake Mono, 

 which was then far more extensive and higher than now. Parallel mo- 

 raines, 300 feet high, formed by the dropping of glacial debris on each 

 side of the icy tongue, as it ran out on the plain or on the bottom of 

 the shallow lake, are very conspicuous, as are also the successive ter- 

 minal moraines left in the subsequent retreat. Behind these moraines 

 water has accumulated, forming lakelets. 



* Undoubted marks of ancient glaciers are found about Berkeley, 300 feet above the 



