ted.
The eruption undoubtedly melted the ice in the vicinity, but after
it had ceased and the rocks had become cold, the glacier never gained
strength enough to push the loose materials of the volcanic cone out
of its path. The ice banked up snugly against the obstruction, and
as it melted the water found its way out at the side of the lava.

Although the surface of the glacier appears at first to offer an
easy route to the higher mountain slopes, yet there are numerous
hidden crevices into which one may fall. The safest arrangement
is to tie a company of people together with a stout rope, so that
if one falls into a crevice the rope will save him. Toward the
middle of the glacier the ice becomes so badly fissured that it is
necessary to turn toward the right margin. There are two sets of
these fissures, one parallel to the direction in which the glacier
is moving, the other at right angles. They are due to the strain
to which the ice is subjected as it moves along at an uneven rate
and over a surface composed of hollows and ridges.

[Illustration: FIG. 18.--MORAINE AT THE END OF THE GLACIER]

Leaving the glacier, we climb upon a long low ridge of gravel and
boulders mixed with fragments of ice. The fragments of rock which
have fallen upon the surface of the ice or been torn from the rock
over which it is moving, have been heaped up along its sides somewhat
as a ridge of snow is raised along each side of the course of a
snow-plough. Such a ridge of debris along the side of a glacier
is known as a marginal moraine. A similar ridge, formed by the
accumulation of rock fragments at the lower end of the glacier,
is a terminal moraine. These ridges and hollows formed by the ice
are found all over the northern portion of the United States. The
hollows once filled with ice are now occupied by the beautiful
lakes of this portion of our country.

As we climb along the moraine at the margin of the glacier, many
openings appear in the clear green ice. There is the sound of gurgling
waters, and occasionally pieces of ice and rock fall into dimly
outlined caverns which are narrow at the top, but far below widen
out to the proportion of chambers.

After the head of the glacier is attained there is still a hard
climb over the snow-fields, which extend upward so far that they
seem to have no end. When at last the gap between the peaks is
gained we are completely tired out. The summit of the middle Sister
rising directly above us