ps by a slower
flowing river. In this part of its course the likeness of a glacial
stream to one of fluid water is manifest. We see that it twists with
the turn of the gorge, widens where the confining walls are far apart,
and narrows where the space is constricted. Although the surface is
here and there broken by fractures, it is evident that the movement of
the frozen current, though slow, is tolerably free. By placing stakes
in a row across the axis of a glacier, and observing their movement
from day to day, or even from hour to hour if a good theodolite is
used for the purpose, we note that the movement of the stream is
fastest in the middle parts, as in the case of a river, and that it
slows toward either shore, though it often happens, as in a stream of
molten water, that the speediest part of the current is near one side.
Further observations have indicated that the movement is most rapid on
the surface and least at the bottom, in which the stream is also
riverlike. It is evident, in a word, that though the ice is not fluid
in strict sense, the bits of which it is made up move in substantially
the manner of fluids--that is, they freely slip over each other. We
will now turn our attention to some important features of a detailed
sort which glaciers exhibit.

If we visit a glacier during the part of the year when the winter
snows are upon it, it may appear to have a very uninterrupted surface.
But as the summer heat advances, the mask of the winter coating goes
away, and we may then see the structure of the ice. First of all we
note in all valley glaciers such as we are observing that the stream
is overlaid by a quantity of rocky waste, the greater part of which
has come down with the avalanches in the manner before described,
though a small part may have been worn from the bed over which the ice
flows. In many glaciers, particularly as we approach their
termination, this sheet of earth and rock materials often covers the
ice so completely that the novice in such regions finds it difficult
to believe that the ice is under his feet. If the explorer is minded
to take the rough scramble, he can often walk for miles on these
masses of stone without seeing, much less setting foot on any frozen
water. In some of the Alaskan glaciers this coating may bear a forest
growth. In general, this material, which is called moraine, is
distributed in bands parallel to the sides of the glaciers, and the
strips may amount to a half