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CHAPTER V.

WAS IT CAUSED BY GLACIERS?

WHAT is a glacier? It is a river of ice, crowded by the weight of
mountain-ice down into some valley, along which it descends by a
slow, almost imperceptible motion, due to a power of the ice, under
the force of gravity, to rearrange its molecules. It is fed by the
mountains and melted by the sun.

The glaciers are local in character, and comparatively few in number;
they are confined to valleys having some general slope downward. The
whole Alpine mass does not move down upon the plain. The movement
downward is limited to these glacier-rivers.

The glacier complies with some of the conditions of the problem. We
can suppose it capable of taking in its giant paw a mass of rock, and
using it as a graver to carve deep grooves in the rock below it; and
we can see in it a great agency for breaking up rocks and carrying
the _detritus_ down upon the plains. But here the resemblance ends.

That high authority upon this subject, James Geikie, says:

"But we can not fail to remark that, although scratched and polished
stones occur not infrequently in the frontal moraines of Alpine
glaciers, yet at the same time these moraines _do not at all resemble
till_. The moraine consists for the most part of a confused heap of
rough _angular_ stones and blocks, and loose sand and _débris_;