Tlie western mountain system of the United States consists
of many ranges, running nearly north and south. The Coast
Range, the Sierra Nevada, the Cascade Mountains, and the
Rocky Mountains extend over about one thousand miles, en-
closing elevated plateaus of very arid lands. This system is
widest at about the latitude of forty degrees.
The term Rocky Mountains is sometimes used to denote all the moun-
tain chains between the Plains and the Pacific Ocean; but strictly it
applies only to the most eastern of these ranges.
The plateaus between these ranges are broken by smaller
ranges, extending mostly in the same direction as the main
ranges.
West of the Sierra Nevada and Cascade Mountains is the
Pacific slope.
DBAINAGE. 59

Between the Rocky Mountains on the west and the Appa-
lachians on the east is the Cheat Central Plain, or Basin of the
Mississippi, containing more than two-fifths of the territory
and more than half of the population of the United States.
38. Drainage.
The Atlantic slope is well watered. Numerous small rivers
rush rapidly down this slope to the Atlantic Ocean. What
is their general course ? At what place in these streams are
rapids found?

The most important rivers of this slope are the Connecticut,
the Hudson, the Delaware, the Susquehanna, and the Po-
tomac.
The Central Plain is drained chiefly by the Mississippi.
This is the largest river in North America, and is about
2900 miles long. The chief tributaries of the Mississippi
are the Ohio on the east, and the Red, the Arkansas, and
the Missouri on the west.
The Mississippi rises in the central part of Minnesota, in Itasca Lake,
or in some feeders of this lake.
