336 J. LeConte—Ancient Glaciers of the Sierras. 
It is perfectly evident from the direction of the scorings 
observed by myself and by Mr. Hawkins, that a great glacier 
came down from the snowy peaks to the southward, and, gath- 
ering tributaries from the peaks on either side but especially 
from the eastern crest, filled the whole basin of the three val- 
leys, forming an immense mer de glace 15 miles long and 8 or 4 
miles wide, which, being blocked to the northward by high 
mountains, themselves probably contributing their share of ice, 
turned at right angles and escaped eastward to the plains of 
Carson, by the deep narrow gorge of Carson cafion. 
V. Lake Vatiey GLACIER. 
From Hope valley our party passed westward over a low 
ridge of debris, then through a cross valley nearly filled with a 
shallow lake and its surrounding marsh and meadow, and then 
down into Lake valley. The ridge of debris is about 600 feet 
above Hope valley, and 100 feet above the cross valley. 
Although I could not find the clear evidences of glaciated sur- 
faces, yet I feel almost sure that the Hope valley mer de glace 
found a second outlet to the west through this cross valley mto 
Lake valley. The debris pile spoken of is, I think, a lateral 
moraine of Hope valley glacier, formed at a later period, when 
this higher outlet had dried up. 
Lake valley heads apparently in the same region of snowy 
summits as Hope valley. The two 
at one time a great glacier came down from the south, filling 
the whole Lake valley for 20 miles, then filling the great basin 
of Lake Tahoe 25 miles long, 15 miles wide, and 1600 feet 
deep, and finally escaped northward and eastward by the 
‘Truckee cafion. “Both Lake valley and Lake Tahoe are flanked 
on either side by high mountains: this great mer de glace there- 
_ fore received tributaries at ever 
