Some cut deep and square, others with flutings and bevelings, or curves, but each helps in the great work of planing off, in some way, the rocky masses over which they move.

Hence it will be seen that the grooving and marking, the fluting and beveling, the planing and smoothing processes of the ice are materially aided and abetted by the very hardness and weight of the granite and other rocks it carries with it.
Now let Joseph LeConte take up the theme and give us of the rich treasure-store of his knowledge and observation.

In the _American Journal of Science and Arts_, Third Series, for 1875, he discussed the very field we are now interested in, and his fascinating and illuminating explanations render the subject perfectly clear.

Said he: Last summer I had again an opportunity of examining the pathways of some of the ancient glaciers of the Sierra.

One of the grandest of these is what I call the _Lake Valley Glacier_.[1] Taking its rise in snow fountains among the high peaks in the neighborhood of Silver Mountain, this great glacier flowed northward down Lake Valley, and, gathering tributaries from the summit ridges on either side of the valley, but especially from the higher western summits, it filled the basin of Lake Tahoe, forming a great "mer de glace," 50 miles long, 15 miles wide, and at least 2000 feet deep, and finally escaped northeastward to the plains.