indstone, millstone, emery stone, mineral
paints, talc and salt, there seems to be enough to meet the needs of the
future as well as the present. Such supplies as sulphur, asphalt,
magnesia, borax, and asbestos, as well as coal and iron, are not very
plentiful. If used carelessly, they will be exhausted in a few years; if
wisely, they may be expected to last beyond the limits of the present
century.

Our supplies of quicksilver, antimony, graphite, mica, tin, nickel,
platinum, and many minerals less well known, as well as our petroleum,
natural gas, copper, gold, silver, lead, zinc, and phosphate rock will
be almost exhausted well within the present century unless large new
deposits are discovered.

REFERENCES

Report of National Conservation Commission.

The Conservation of Mineral Resources. U. S. Government Reports.

Report of the U. S. Geological Survey.

Production of Gold in 1908. U. S. Government Reports.

Production of Silver in 1908.

Production of Lead in 1908.

Production of Zinc in 1908.

Production of Structural Materials.

About twenty pamphlets on other minerals.

CHAPTER IX

ANIMAL FOODS

GRAZING

Food is of two classes: vegetable, which comes directly from the earth,
and animal, which has fed on vegetable life. This is, of course, a more
concentrated form of food, and much less of it is needed to sustain
life.

For the plentiful supply of vegetable food we must depend upon the
fertility of the soil, as we have seen. Our animal food can not be
classed among our natural resources, but as a product of them, and
requires the same care and wise use.

In the early history of our country natural animal food was abundant.
Fishes swarmed in the sea, lakes, and streams. Wild turkeys and other
game birds, deer, and bison formed a large part of the food of our
forefathers. But these have been gradually disappearing. We have caught
and destroyed so many fish that we have only a fraction of our former
number. The game birds have disappeared either because they have been
killed in great numbers or because their nesting-places have been
destroyed. Of the big game nothing is now left except in a few remote
regions, and it is growing less plentiful each year.

Although large quantities of fish and game are marketed every year at
certain seasons, they form a small fraction of the animal food required
in the country, and we must now depend for most of our animal food, not
on that which w