Cockscomb Crest 



23 



expected the extensive and deep ice-fields and glaciers of the 

 earlier epoch to have come from a Sierra crest completely 

 domed over with smoothly sloping, unbroken snow-fields, and 

 the relatively modest ice-streams of the later epoch to have 

 flowed forth from cirques filled only to moderate depth, and 

 partitioned from one another by bare rock crests and "arretes" 

 rising high above the ice; but, curiously, it appears that the 

 snow conditions along the Sierra crest were substantially the 

 same in both epochs. The snows that fed the vast glaciers of 

 the earlier epoch filled the summit cirques to no greater depth 

 than did the snows that formed the smaller glaciers of the later 

 epoch. The significance of this remarkable coincidence need 

 not be here discussed — it would lead too far afield; suffice it 

 for our purpose that the fact has been established. 



A few figures will help to give more definiteness to one's 

 conception of the relation of the two ice-Unes. The later Yo- 

 semite Glacier ended at the Bridal Veil Meadows at an altitude 

 of 3900 feet, but the lateral moraines left by the earlier ice- 

 stream on either side of the Yosemite chasm lie 2700 feet above 

 this spot. At the head of the valley the later glacier attained a 

 depth of about 1500 feet, but the lateral moraines of the earlier 

 glacier still lie 2400 feet higher. Within the next few miles 

 the two ice-lines converge with remarkable rapidity. In the 

 Little Yosemite, for instance, they are only 600 feet apart. 

 There the later ice rose within 100 feet of the top of Moraine 

 Dome, but the earlier ice passed over it with a depth of over 

 500 feet. Opposite Lake Merced the difference in altitude be- 

 tween the two ice-lines dwindles to 400 feet, and thence up- 

 ward, to the ultimate source of the glacier under Mount Lyell, 

 the difference steadily decreases until it becomes a vanishing 

 quantity. 



Following the ice-lines up through Tenaya Cafion, they are 

 found to be 2100 feet apart in altitude opposite Half Dome. 

 That rock monument was engulfed by the earlier ice up to 

 within 700 feet of its summit, but even the foot of its great 

 cliff rose 800 feet above the surface of the later glacier. At the 

 head of Tenaya Canon the earlier ice rose only 900 feet higher 

 than the later ice, and still farther up, on the divide between 

 the Tenaya and Tuolumne basins, the two ice-lines are only 400 



