f peneplains
that they trace ranges long ages washed away. History may, in some dim
future age, repeat still another wonder, for upon the flattened wreck of
the Front Range may rise, by some earth movement, a new and even nobler
range.

But what about the precipitous eastern front?

That masterpiece was begun by water, accomplished by ice, and finished
by water. In the beginning, streams determined the direction of the
valleys and carved these valleys deep. Then came, in very recent times,
as geologists measure earth's history, the Great Ice Age. As a result of
falling temperature, the mountains became covered, except their higher
summits and the continental divide, with glaciers. These came in at
least two invasions, and remained many hundreds of thousands of years.
When changing climate melted them away, the Rocky Mountain National Park
remained not greatly different from what it is to-day. Frosts and rains
have softened and beautified it since.

These glaciers, first forming in the beds of streams by the
accumulations of snow which presently turned to ice and moved slowly
down the valleys, began at once to pluck out blocks of granite from
their starting-points, and settle themselves in cirques. They plucked
downward and backward, undermining their cirque walls until falling
granite left precipices; armed with imprisoned rocks, they gouged and
scraped their beds, and these processes, constantly repeated for
thousands of centuries, produced the mountain forms, the giant gorges,
the enormous precipices, and the rounded granite valleys of the
stupendous east elevation of the Front Range.

There is a good illustration in Iceberg Lake, near the base of Trail
Ridge on the Ute Trail. This precipitous well, which every visitor to
Rocky Mountain should see, originally was an ice-filled hollow in the
high surface of the ridge. When the Fall River Glacier moved eastward,
the ice in the hollow slipped down to join it, and by that very motion
became itself a glacier. Downward and backward plucking in the cirque
which it presently made, and the falling of the undermined walls,
produced in, say, a few hundred thousand years this striking well, upon
whose lake's surface visitors of to-day will find cakes of floating ice,
broken from the sloping snow-field which is the old glacier's remainder
and representative of to-day.

The glaciers which shaped Rocky Mountain's big canyons had enormous size
and thickness. Ice streams from sc