oversweeping ice from the north and northwest, and their surfaces have a
smooth, rounded, overrubbed appearance, generally free from angles. The
intricate labyrinth of canals, channels, straits, passages, sounds,
narrows, etc. between the islands, and extending into the mainland, of
course manifest in their forms and trends and general characteristics
the same subordination to the grinding action of universal glaciation as
to their origin, and differ from the islands and banks of the fiords
only in being portions of the pre-glacial margin of the continent more
deeply eroded, and therefore covered by the ocean waters which flowed
into them as the ice was melted out of them. The formation and extension
of fiords in this manner is still going on, and may be witnessed in many
places in Glacier Bay, Yakutat Bay, and adjacent regions. That the
domain of the sea is being extended over the land by the wearing away of
its shores, is well known, but in these icy regions of Alaska, and even
as far south as Vancouver Island, the coast rocks have been so short a
time exposed to wave-action they are but little wasted as yet. 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°. 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