ey flowed here and there building up
the plateau, frequently broke up the rivers and turned them into
new channels. As time went on the eruptions were less violent, and
the rivers became established in the channels which they occupy
to-day. The Columbia River, winding about over the plateau, sought
the easiest path to the sea. It soon began to dig a channel, and
now has hidden itself between dark walls of lava.

But other forces besides the streams were now at work in this volcanic
region. The lava plateau began slowly to bend upward along the
line of the great volcanoes, lifting them upward with it. In this
manner the Cascade Range was formed. The Columbia River, instead
of seeking another way to the sea, continued cutting its channel
deeper and deeper into the growing mountain range, and so has given
us that picturesque canon which forms a most convenient highway
from the interior of Washington and Oregon to the coast.

Take a sheet of writing paper, lay it upon an even surface, then
slowly push the opposite edges toward each other. This simple experiment
will aid one in understanding one of the ways in which mountain
ranges are made. Besides the upward fold of the plateau which made
the Cascade Range, another was formed between the Blue Mountains
in eastern Oregon and a spur of the Rocky Mountains in northern
Idaho. This fold lay across the path of the Snake River, but its
movement was so slow that the river kept its former channel and
in this rising land excavated a canon which to-day is more than
a mile deep. The upper twenty-five hundred feet of the canon are
cut into the lava of the plateau, and the lower three thousand
into the underlying granite. The canon is not so picturesque as
the Colorado, for it has no rocks with variegated coloring or
castellated walls. Its sides are, however, exceedingly precipitous
and it is difficult to enter.

[Illustration: FIG. 10.--SHOSHONE FALLS, SNAKE RIVER, IDAHO]

Along portions of the lower Columbia and Snake rivers, navigation
is obstructed by rapids and waterfalls. The presence of these falls
teaches us that these streams are still at work cutting their channels
deeper. The Snake River in its upper course has as yet cut only a
very shallow channel in the hard lava, and the beautiful Shoshone
Falls marks a point where its work is slow. These falls, which
are the finest in the northwest, owe their existence to the fact
that at this particular spot layers of strong resist