ow of frost and heat help greatly to tear down the
cliffs. Thus marginal moraines built of the debris begin to form, on
the ice, far up the side of the peak. As the glacier advances, driven
by its weight and the resistless mass of snow above, it is often
joined by another glacier, bringing its own marginal moraines. Where
the two meet, a medial moraine results. (See illustrations, pp. 68 and
77.) Some medial moraines are many feet high. Trees are found growing
on them. In Switzerland houses are built upon them. Often the debris
which they transport, as the ice carries them forward, includes rocks
as big as a ship.

[Illustration: One of the bedrooms at Camp Muir.]

[Illustration {p.084}: A perilous position on the edge of a great
crevasse. Cowlitz Glacier, near end of Cathedral Rocks.]

A glacier's flow varies from a hundred to a thousand feet or more a
year, depending upon {p.085} its volume, its width, and the slope of
its bed. As the decades pass, its level is greatly lowered by the
melting of the ice. More and more, earth and rocks accumulate upon the
surface, as it travels onward, and are scattered over it by the rains
and melting snow. At last, in its old age, when far down its canyon,
the glacier is completely hidden, save where crevasses reveal the ice.
Only at its snout, where it breaks off, as a rule, in a high wall of
ice, do we realize how huge a volume and weight it must have, far
above toward its sources, or why so many of the crevasses on the upper
ice fields seem almost bottomless.

[Illustration: Climbing the "Chute," west side of Gibraltar. Here the
guides cut steps in the ice.]

These hints of the almost inconceivable mass of a glacier, with its
millions of millions of tons, suggest how much of the Mountain has
already been whittled and planed away. But here we may do better than
speculate. The original surface of the peak is clearly indicated by
the tops of the great rocks which have survived the glacial
sculpturing. These rise from one to two thousand feet above the
glaciers, which are themselves several thousand feet in depth. The
best known of them is the point formed by Gibraltar and the ridges
that stretch downward from it, Cowlitz Cleaver and Cathedral Rocks,
making a great inverted V. Eastward of this, another V with its apex
toward the summit, is called Little Tahoma; and beyond, still another,
Steamboat Prow, forming the tip of "The Wedge."

Spines of rock like these are found on all