birds to nest.

Wrens, bluebirds, chickadees, martins, and some other varieties are all
glad to set up housekeeping in man-made houses. The proper size for a
bird-room is easily remembered. Give each room six square inches of
floor space and make it eight inches high. Old, weathered boards should
be used; or, if paint is employed, a dull color to resemble an old
tree-trunk will be most inviting. A single opening near the top should
be made two inches in diameter for the larger birds; but if the house is
to be headquarters for the wren, a one-inch opening is quite large
enough, and the small door serves all the better to keep out English
sparrows.

The barn attic should be turned over to the swallows. Small holes may be
cut high up in the gables and left open during the time that the
swallows remain with us. They will more than pay for shelter by the good
work they do in ridding the barn of flies, gnats, and mosquitoes.

SECTION LXVIII. FARMING ON DRY LANDS

Almost in the center of the western half of our continent there is a
vast area in which very little rain falls. This section includes nearly
three hundred million acres of land. It stretches from Canada on the
north into Texas on the south, and from the Missouri River (including
the Dakotas and western Minnesota) on the east to the Rocky Mountains on
the west. In this great area farming has to be done with little water.
This sort of farming is therefore called "dry-farming."

The soil in this section is as a rule very fertile. Therefore the
difference between farming in this dry belt and farming in most of the
other sections of our country is a difference mainly due to a lack of
moisture.

As water is so scarce in this region two things are of the utmost
importance: first, to save all the rain as it falls; second, to save all
the water after it has fallen. To save the falling rain it is necessary
for the ground to be in such a condition that none of the much-needed
rain may run off. Every drop should go into the soil. Hence the farmer
should never allow his top soil to harden into a crust. Such a crust
will keep the rain from sinking into the thirsty soil. Moreover the soil
should be deeply plowed. The deeper the soil the more water it can hold.
The land should also be kept as porous as possible, for water enters a
porous soil freely. The addition of humus in the form of vegetable
manures will keep the soil in the porous condition needed. Second, after
the w