Let us consider the facts.

Some of them are well known, and the salient ones can be put very briefly.
The five indispensably essential materials in our civilization are wood, water, coal, iron, and agricultural products.
We have timber for less than thirty years at the present rate of cutting.

The figures indicate that our demands upon the forest have increased twice as fast as our population.
We have anthracite coal for but fifty years, and bituminous coal for less than two hundred.
Our supplies of iron ore, mineral oil, and natural gas are being rapidly depleted, and many of the great fields are already exhausted.

Mineral resources such as these when once gone are gone forever.
We have allowed erosion, that great enemy of agriculture, to impoverish and, over thousands of square miles, to destroy our farms.

The Mississippi alone carries yearly to the sea more than 400,000,000 tons of the richest soil within its drainage basin.