s, dug out the canon. This glacier was over three thousand feet
in thickness, for the rocks are grooved and polished to a height
of nearly two thousand feet above the surface of the water. It
is, nevertheless, improbable that the glacier did anything more
than deepen and widen the canon somewhat. It was certainly made,
as we at first supposed, by a river which flowed through it at
some remote period. At that time the land of our Pacific coast must
have stood many hundred feet higher than it does now.

[Illustration: FIG. 59.--GOAT MOUNTAIN, NORTH SHORE OF LAKE CHELAN]

The surface of Lake Chelan is a little more than three hundred
feet above the bed of the Columbia River, which flows through a
deep canon only three miles distant. If we could remove the dam
of glacial boulders and gravel at the lower end of the lake, the
water would be lowered only three hundred feet. The lake would
not be drained, for it is very much deeper. Now here is another
puzzle for us: the bottom of the lake is more than one thousand
feet below the level of the Columbia. We shall have to go still
farther back into the past to get a satisfactory explanation this
time.

Hundreds of thousands of years ago there was no plateau filling
central Washington, and no Columbia River crossing it. The Cascade
Range stood where we see it to-day, and the region of the plateau
was a broad valley, toward which flowed the streams that had already
cut canons upon the eastern side of the range. These streams probably
united in a river emptying westward into the Pacific by a course
now unknown. The shores of the ocean were farther west than at
present, for the land stood higher.

The canon of Lake Chelan was made by a river of this period, which
through many long years gradually deepened and enlarged its channel.
The river worked just as we see rivers working at the present time,
for throughout all the history of the earth rivers have not changed
their habits. Then came the long period of volcanic eruptions. Our
Northwest was flooded by fiery lava, which built up the Columbia
plateau and buried under thousands of feet of rock the old river
valley into which the canon of Chelan emptied.

Then streams of water began to flow over the plateau from the higher
mountains above the reach of the lava. These streams formed the
Columbia River, which sought the easiest way to the sea, and finally
excavated a canon for hundreds of miles. In a portion of its course
the rive