In these
regions the extension of the sea effected by its own action in
post-glacial time is scarcely appreciable as compared with that effected
by ice-action.
Traces of the vanished glaciers made during the period of greater
extension abound on the Sierra as far south as latitude 36 deg.. Even the
polished rock surfaces, the most evanescent of glacial records, are
still found in a wonderfully perfect state of preservation on the upper
half of the middle portion of the range, and form the most striking of
all the glacial phenomena. They occur in large irregular patches in the
summit and middle regions, and though they have been subjected to the
action of the weather with its corroding storms for thousands of years,
their mechanical excellence is such that they still reflect the sunbeams
like glass, and attract the attention of every observer. The attention
of the mountaineer is seldom arrested by moraines, however regular and
high they may be, or by canons, however deep, or by rocks, however noble
in form and sculpture; but he stoops and rubs his hands admiringly on
the shining surfaces and trios hard to account for their mysterious
smoothness.
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