-level; somewhat higher than this toward the
southern extremity of the range, lower toward the northern, on account
of the difference in time of the withdrawal of the glaciers, due to
difference in climate. Specimens occur here and there considerably below
this limit, in basins specially protected from inwashing detritus, or
exceptional in size. These, however, are not sufficiently numerous to
make any marked irregularity in the line. The highest I have yet found
lies at an elevation of about 12,000 feet, in a glacier womb, at the
foot of one of the highest of the summit peaks, a few miles to the north
of Mount Hitter. The basins of perhaps twenty-five or thirty are still
in process of formation beneath the few lingering glaciers, but by the
time they are born, an equal or greater number will probably have died.
Since the beginning of the close of the ice-period the whole number in
the range has perhaps never been greater than at present.

A rough approximation to the average duration of these mountain lakes
may be made from data already suggested, but I cannot stop here to
present the subject in detail. I must also forego, in the mean time, the
pleasure of a full discussion of the interesting question of lake-basin
formation, for which fine, clear, demonstrative material abounds in
these mountains. In addition to what has been already given on the
subject, I will only make this one statement. Every lake in the Sierra
is a glacier lake. Their basins were not merely remodeled and scoured
out by this mighty agent, but in the first place were eroded from the
solid.

I must now make haste to give some nearer views of representative
specimens lying at different elevations on the main lake-belt, confining
myself to descriptions of the features most characteristic of each.

SHADOW LAKE

This is a fine specimen of the oldest and lowest of the existing lakes.
It lies about eight miles above Yosemite Valley, on the main branch of
the Merced, at an elevation of about 7350 feet above the sea; and is
everywhere so securely cliff-bound that without artificial trails only
wild animals can get down to its rocky shores from any direction. Its
original length was about a mile and a half; now it is only half a mile
in length by about a fourth of a mile in width, and over the lowest
portion of the basin ninety-eight feet deep. Its crystal waters are
clasped around on the north and south by majestic granite walls
sculptured in true Yo