ortant function which the river does not
share. Far up at its beginnings it freezes to the back wall of its
cirque, and, moving forward, pulls out, or plucks out, as the
geologists have it, masses of rock which it carries away in its current.
The resulting cavities in the back of the cirque fill with ice, which in
its turn freezes fast and plucks out more rock. And presently the back
wall of the cirque, undermined, falls on the ice and also is carried
away. There is left a precipice, often sheerly perpendicular; and, as
the process repeats itself, this precipice moves backward. At the
beginning of this process, it must be understood, the glacier lies upon
a tilted surface far more elevated than now when you see it in its old
age, sunk deep in its self-dug trench; and, while it is plucking
backward and breaking off an ever-increasing precipice above it, it is
plucking downward, too. If the rock is even in structure, this downward
cutting may be very nearly perpendicular, but if the rock lies in strata
of varying hardness, shelves form where the harder strata are
encountered because it takes longer to cut them through; in this way are
formed the long series of steps which we often see in empty glacial
cirques.

By this process of backward and downward plucking, the Carbon Glacier
bit its way into the north side of the great volcano until it invaded
the very foundations of the summit and created the Willis Wall which
drops avalanches thirty-six hundred feet to the glacier below. Willis
Wall is nearly perpendicular because the lava rock at this point was
homogeneous. But in the alternating shale and limestone strata of
Glacier National Park, on the other hand, the glaciers of old dug
cirques of many shelves. The monster ice-streams which dug Glacier's
mighty valleys have vanished, but often tiny remainders are still seen
upon the cirques' topmost shelves.

[Illustration: _From a photograph by Asahel Curtis_

MOUNT RAINIER AND PARADISE INN IN SUMMER]

[Illustration: _From a photograph by Jacobs_

WINTER PLEASURES AT PARADISE INN, MOUNT RAINIER]

So we see that the glacier acquires its cargo of rock not only by
scraping its sides and plucking it from the bottom of its cirque and
valley, but by quarrying backward till undermined material drops upon
it; all of this in fulfilment of Nature's purpose of wearing down the
highlands for the upbuilding of the hollows.

This is not the place for a detailed description of Mount