ake River plains, which must have been, when first
formed, hundreds of miles long, seventy-five miles wide, and almost
as even as a floor. If we could have looked on while these things
were taking place it would have appeared as if the whole land was
about to sink under the fiery mass which flowed out of the earth.
The streams and valleys were completely buried. The region of the
John Day Lake, with all its animal remains, was covered. The lava,
like a sea, crept up against the mountains surrounding the plateau
region. Bays of lava extended into the valleys among the mountains,
while mountain ridges rose like islands and capes from the surface
of the flood.

We never tire of looking at the lofty snow-capped peaks of the
Cascade Range. A dozen of them rise over ten thousand feet, and
two, Mounts Shasta and Ranier, are more than fourteen thousand
feet high. All these mountains were formed of material thrown out
of the interior of the earth during the building of the Columbia
plateau. The process was very similar for each. About some one
exceptionally active crater immense quantities of scoriae[1] and
lapilli[2] accumulated. Then came streams of fiery lava, some of
which, hardening upon the outer slopes of the crater, added still
more to the growth of the mountain. The process was very slow,
however. A time of eruption, marked by tremblings of the earth,
explosive noises, and a sky filled with dust and clouds, might last
for many years. Then came a long period of rest when the falling
rains, gathering in dashing torrents, cut deep gullies down the
sides of the mountain.

[Footnote 1: _scorioe_, cellular, slaggy lava.]

[Footnote 2: _lapilli_, volcanic ashes, consisting of small, angular,
stony fragments.]

[Illustration: FIG. 9.--PITT RIVER CANON, NORTHERN CALIFORNIA

The plateau is built of layers of lava]

The volcanoes at last ceased to grow any higher, for the lava,
if the eruptions continued, formed new craters at their bases.
It is probable that all these great peaks have been extinct for
several thousand years, although some are much older and more worn
away than others. One of these volcanoes has completely disappeared,
and in its place lies that wonderful sheet of water known as Crater
Lake. It is thought that the interior of this mountain was melted
away during a period of activity, and that the outer portion fell
in, leaving a crater five miles across and nearly a mile deep.

The streams of lava, as th