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.