Remembering that ice is a hard and brittle solid, it comes as a surprise
to find that it can flow like a plastic body under the pull of gravity;
but this can be easily proved. A row of stakes or of metal plates put
across a glacier gradually gets out of line, the middle parts moving
fastest as in a river; but the motion is very slow, even in the middle,
seldom more than a few inches a day in our mountain glaciers, though
some of the great Alaskan and Greenland glaciers are reported to move
several feet a day and in one or two cases as much as 60 or 70 feet.
[Illustration]