rried along with it will be
caught there, and form a deposit at the bottom of the hole. As day after
day, throughout the summer, the rivulet is renewed, it carries with it
an additional supply of these light materials, until the opening is
gradually filled and the sand is brought to a level with the surface of
the ice. We have already seen, that, in consequence of evaporation,
melting, and other disintegrating causes, the level of the glacier sinks
annually at the rate of from five to ten feet, according to stations.
The natural consequence, of course, must be, that the sand is left
standing above the surface of the ice, forming a mound which would
constantly increase in height in proportion to the sinking of the
surrounding ice, had it sufficient solidity to retain its original
position. But a heap of sand, if unsupported, must very soon subside and
be dispersed; and, indeed, these pyramids, which are often quite lofty,
and yet look as if they would crumble at a touch, prove, on nearer
examination, to be perfectly solid, and are, in fact, pyramids of ice
with a thin sheet of sand spread over them. A word will explain how this
transformation is brought about. As soon as the level of the glacier
falls below the sand, thus depriving it of support, it sinks down and
spreads slightly over the surrounding surface. In this condition it
protects the ice immediately beneath it from the action of the sun. In
proportion as the glacier wastes, this protected area rises above the
general mass and becomes detached from it. The sand, of course, slides
down over it, spreading toward its base, so as to cover a wider space
below, and an ever-narrowing one above, until it gradually assumes the
pyramidal form in which we find it, covered with a thin coating of sand.
Every stage of this process may occasionally be seen upon the same
glacier, in a number of sand-piles raised to various heights above the
surface of the ice, approaching the perfect pyramidal form, or falling
to pieces after standing for a short time erect.

The phenomenon of the large boulders, supported on tall pillars of ice,
is of a similar character. A mass of rock, having fallen on the surface
of the glacier, protects the ice immediately beneath it from the action
of the sun; and as the level of the glacier sinks all around it, in
consequence of the unceasing waste of the surface, the rock is
gradually left standing on an ice-pillar of considerable height. In
proportion