182 J. LeConte—Ancient Glaciers of the Sierra Nevada. 
sweeps again up the cafion-beds, little lakes, glacier scooped 
rock basins, filled with ice-cold water, flash in the sunlight on 
every side. ‘T'welve or fifteen of these may be seen. 
From appropriate positions on the surface of Lake Tahoe, 
also, all the moraine ridges are beautifully seen at once, but 
so 
the general position of the rocky points, and the moraine 
ridges, are tolerably correct. But, otherwise, the sketch is in- 
tended as an illustrative diagram rather than a topographical 
map. iew is supposed to be taken from an elevated 
position above the lake surface, looking southward. 
There are several questions of a general nature suggested by 
my examination of these three glacial pathways, which I have 
thought best to consider separately. 
a. Hvidences of the existence of the Great Lake Valley Glacier.— 
In my former paper I have already given some evidence of the 
former existence of this glacier in the glacial forms detectable in 
the upper part of this valley. I will now give some additional 
evidence, gathered last summer. 
n the south shore of Lake Tahoe, and especially at the 
northern or lower end of Fallen Leaf Lake, I found many 
rock of these aie and boulders. It is a powerful outcrop- 
ping ledge of beautifully striped siliceous slate, full of fissures 
and joints, and easily broken into blocks of all sizes, crossing 
the cafion about a half mile above the lake. This rock is so 
peculiar and so easily identified that its fragments become an 
admirable index of the extent of the glacial transportation. I 
have, myself, traced these pebbles only a little way along the 
western shores of the great lake, as my observations were 
pinay confined to this part; but I learn from my brother, 
-rofessor John LeConte, and from Mr. John Muir, both o 
whom have examined the pebbles I brought home, that pre- 
cisely similar fragments are found in great abundance all — 
the western shore from Sugar Pine Point northward, an 
especially on the extreme northwestern shore nearly thirty 
miles from their source. I have visited the eastern shore of 
the lake somewhat more ‘extensively than the western, and 
