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bottom of the glacier where it rests upon its rock
bed. Another downward moving action has been
recently explained by Dr. Croll. It is that of an
actual downward transfer of the substance of the
glacier by the regelation above described. Every
particle of water which descends as water thawed
on the surface, and becomes ice refrozen lower
down, represents a downward motion of so much
of the body of the glacier.
Thus we have the down-flow of a plastic mass,
the down-thrust of a mass expanding interiorly,
and the down-growth of regelation, or solid
convection downwards, all conspiring to move the
glacier in one direction, viz. from its upper source
towards its terminal outlet.
If the above description of glacial forces is
correct, the flowing of glaciers should be demonstrable
by their actual and visible motion. This is the
case. All glaciers move or flow slowly down the
valleys containing them, and this motion has been
carefully investigated. It is found to resemble the
flow of a river, being more rapid at the middle
than at the sides. It increases with the slope, and
varies with the temperature, being much faster in
summer than in winter, during the day than at
night. It varies from two or three inches to two
or three feet per day. The plastic nature of the
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