ly barren valleys
was poor, but such is not the case. The ground did not lack plant
food, but merely the water to make this food available. With plenty
of water the most luxuriant vegetation is produced. The soil is,
indeed, frequently richer than in well-watered regions, for a lavish
supply of water carries away a portion of the plant food.

In some places, where the land is almost level and the soil is
filled with large quantities of soluble materials, such as soda
and salt, keeping the ground moist through irrigation brings these
substances to the surface in such quantities as to injure and sometimes
kill the vegetation. In order that such lands may be successfully
cultivated, the salts have to be either neutralized or washed away.

[Illustration: FIG. 117.--IRRIGATING DITCH, NEAR PHOENIX, ARIZONA]

Many of the rivers of the West carry large quantities of silt in
suspension, which fills the ditches and causes a great deal of
trouble; but when the silt is deposited over the surface it adds
continually to the richness of the land.

The full development of irrigation will mean a great increase in
the population and wealth of all the Western States.

THE LOCATION OF THE CITIES OF THE PACIFIC SLOPE

This old earth has to be consulted upon every occasion. It is a
silent partner in all our undertakings. We sometimes think that
we come and go as we please, but a little thought convinces us
that we are not really so free.

The traveller must take account of the slopes of the land. It is
much easier for him to follow a valley and cross a mountain range
through a low spot, although his course be very crooked, than it is
to make a "bee line" for his destination. The farmer, in choosing
his home and the kind of produce which he will raise, has to consult
the soil and climate. He cannot expect to grow grain where the
soil is poor and dry, or grow apples where the late spring frosts
kill the buds. The miner knows that he cannot expect to find gold
veins in the valleys, where the rocks are deeply covered by the
soil, and so he turns his steps toward the mountains, where Nature
has made his work easy by lifting up the rocks and exposing them
to his view.

Routes of commerce and trade are governed by geographic, and to a
certain extent by climatic, conditions. Shallow streams with rapids
and waterfalls obstruct navigation. The absence of harbors along a
given coast makes it difficult for ships to take and discharge
ca