Page:Popular Science Monthly Volume 14.djvu/356

342 {| Square Miles. Area.
 * width=240 |COUNTRIES.
 * width=130 |Area of Coal-fields in
 * width=130 |Area of Coal-fields in
 * width=130 |Percentage of Total
 * United States
 * 192,000
 * 73.85
 * Nova Scotia
 * 18,000
 * 6.90
 * Great Britain
 * 11,900
 * 4.60
 * Spain
 * 3,000
 * 1.20
 * France
 * 1,800
 * 0.70
 * Prussia
 * 1,800
 * 0.70
 * Austria
 * 1,800
 * 0.70
 * Belgium
 * 900
 * 0.35
 * Chili, Australia, India, China, etc.
 * 28,000
 * 11.00
 * Totals
 * 260,000
 * 100.00
 * }
 * 0.35
 * Chili, Australia, India, China, etc.
 * 28,000
 * 11.00
 * Totals
 * 260,000
 * 100.00
 * }
 * 100.00
 * }
 * }

And now for the story of how this wonderful mineral was formed. It is one of the well-established facts of geology that it is of vegetable origin. This is not simply a theory, for in Nature coal can be seen in various stages of formation where vegetable tissue is heaped up and accumulated in bogs. As we dig down into these bogs where the woody matter is surrounded by moisture, and in a favorable position for slow decomposition, it is seen that it is transformed into a dark, combustible compound which is first called peat; then, as it becomes harder and more changed, lignite; while the oldest peat-bogs in Europe have, at or near their bottom, thin layers of hard, black matter that neither examination by the eye nor analysis by the chemist can distinguish from true coal, and which, therefore, must be true coal. "In Holland, Denmark, and Sweden, the thick deposits of peat are separated into distinct beds by strata of sand and mud, giving the best possible elucidation of the process of stratification of the coal-measures" (Lesquereux). For their formation these bogs require a basin rendered impermeable by a substratum of clay and an active growth of aquatic or semi-aërial plants, having their roots in water, while their branches and leaves expand on the surface thereof, or rise in the air above it, constantly growing in the same place, whose débris, falling year after year, is heaped up and preserved against atmospheric decomposition by stagnant water or great humidity in the air. It was during the Carboniferous epoch, when our principal and most valuable seams of coal were deposited, that all these favorable circumstances were in their highest development. For a dense vegetation we also want a warm, moist, and equable climate, and air more or less charged with carbonic-acid gas, as that is the food of plants (just as the oxygen gives life to man), though it is poisonous to warm-blooded animals, it being impossible for such to live in an atmosphere containing more than about one per cent. of it.

During the Carboniferous age of the earth's history the water covered very much more of area than it now does, and portions of the continents were so little raised above its surface that a slight elevation or depression would change them from marshes and lagoons into dry land, or sink them below the surface of the sea. When air passes over, or rests on, oceans, or lakes, or rivers, etc., it becomes laden with vapor,