y any decrease in the slope of the bed. When a flat, broad
area is reached, a lake of ice may be formed. These are not frequent in
the Alps. The water near the banks and at the bottom of a river does not
flow as swiftly as in the middle and at the surface of the stream. The
flow of ice in a glacier is just so. Friction with the banks and bottom
retards the ice while the middle parts go forward, melting under the
strain, and freezing again. There is a constant readjusting of
particles, which does not affect the solidity of the mass.

The ice moulds itself over any unevenness in its bed if it cannot remove
the obstruction. The drop which would cause a small waterfall in a
river, makes a bend in the thick body of the ice river. Great cracks,
called _crevasses_, are made at the surface, along the line of the bend.
The width of the V-shaped openings depends upon the depth of the glacier
and the sharpness of the bend that causes the breaks.

Rocky ridges in the bed of the ice-stream may cause crevasses that run
lengthwise of the glacier. Snow may fill these chasms or bridge them
over. The hunter or the tourist who ventures on the glacier is in
constant danger, unless he sees solid ice under him. Men rope themselves
together in climbing over perilous places, so that if one slips into a
crevasse his mates can save him.

A glacier tears away and carries away quantities of rock and earth that
form the walls of its bed. As the valley narrows, tremendous pressure
crowds the ice against the sides, tearing trees out by the roots and
causing rock masses to fall on the top of the glacier, or to be dragged
along frozen solidly into its sides. The weight of the ice bears on the
bed of the glacier, and its progress crowds irresistibly against all
loose rock material. The glacier's tools are the rocks it carries frozen
into its icy walls and bottom. These rocks rub against the walls,
grinding off debris which is pushed or carried along. No matter how
heavy the boulders are that fall in the way of the ice river, the ice
carries them along. It cannot drop them as a river of water would do.
Slowly they travel, and finally stop where the nose of the glacier melts
and leaves all debris that the mountain stream, fed by the melting of
the ice, cannot carry away.

The bedrock under a glacier is scraped and ground and scored by the
glacier's tools--the rock fragments frozen into the bottom of the ice.
These rocks are worn away by constant grindi