ACADEMY OF SCIENCES. 43 
There are several questions of a general nature suggested by my examina- 
tion of these three glacial pathways, which I have thought best to consider 
separately. 
a. Evidences 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. 
On the south shore of Lake Tahoe, and especially at the northern or lower 
end of Fallen Leaf Lake, I found many pebbles and some large boulders of a 
beautifully striped, agate-like slate. The stripes consisted of alternate bands, 
of black and translucent white, the latter weathering into milk white, or yel- 
lowish, orreddish. It was perfectly evident that these fragments were brought 
down from the cafton above Fallen Leaf Lake. On ascending this canon I 
easily found the parent rock of these pebbles and boulders. It is a powerful 
outcropping ledge of beautifully striped silicious slate, full of fissures and 
joints, and easily broken into blocks of all sizes, crossing the canon 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 principally 
confined to this pait; but I learn from my brother, Professor John Le Conte, 
and from Mr. John Muir, both of whom have examined the pebbles I brought 
home, that precisely similar fragments are found in great abundance all along 
the western shore from Sugar Pine Point northward, and 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 nowhere did I see similar pebbles. Mr. Muir, who has walked 
around the lake, tells me that they do not occur on the eastern shore. We 
have, then, in the distribution of these pebbles, demonstrative evidence of 
the fact that Falien Leaf Lake glacier was once a tributary of a much greater 
glacier which filled Lake Tahoe. 
The only other agency to which we could attribute this transportation, is 
that of shore ice and icebergs, which probably did once exist on Lake Tahoe; 
but the limitation of the pebbles to the western, and especially the north- 
western shores, is in exact accordance with the laws of glacial transportation, 
but contrary to those of floating ice transportation—for lake ice is carried 
only by winds, and would, therefore, deposit equally on all shores. 
Again: I think I find additional evidence of a Lake Tahoe mer de glace in 
the contrasted character of the northern and southern shores of this lake. 
All the little glacial lakes described above are deep at the upper end and 
shallow at the lower end. Further: all of them have a sand beach and asand 
flat at the upper end, and great boulders thickly scattered in the shallow water, 
and along the shore at the lower end. These facts are easily explained, if we 
remember that while the glacial scooping was principally at the upper end, the 
glacial droopings were principally at the lower end. And further: that while 
the glacial deposit was principally at the lower end, the river deposit, since 
the glacial epoch, has been wholly at the upper end. 
