Europe and the United States to-day produce practically all the coal of the world. In Europe, Great Britain, Germany, France, Austria-Hungary, and Belgium are the main sources of supply. Several important coal areas exist in our own country, notably that of the New England basin, with an area of 500 square miles; the Appalachian district, with an area of 65,000 square miles; the northern area, in Michigan, covering 7,000 square miles; the central area, comprising parts of Illinois, Indiana and Kentucky, and including 48,000 square miles; the scattered western area, with a total of 98,000 square miles; the indefinite Rocky Mountain area, and the Pacific coast region, including parts of California, Oregon, and Washington. Coal mining is yet an undeveloped industry in our territorial possessions. Alaska has an abundant supply of coal, and lesser quantities are found in Cuba and Porto Rico. Mention has already been made of the two common kinds of coal, bituminous and anthracite. These two kinds mark different stages in the transformation from plant organism to mineral product. As the biologist traces the successive steps in the evolution of an individual of a species from germ to adult, so the geologist unfolds before us the wonderful history of a piece of coal from its first appearance on the earth to the time when it is thrown into our fire grate as fuel. Coal is the metamorphosed product of vegetable growths, changed by atmospheric agencies and the internal forces of the earth acting through a total period of perhaps millions of years. In the remote past, ages before man had appeared on the earth, the atmosphere or our globe was highly charged with carbon gases. Vegetation flourished in luxuriance. Great swamps were common. The ocean alternately covered and receded from verdure-clothed land areas. Ponds were transformed to morasses and swamps. In the swamps thus formed, the accumulated sediment of centuries upon centuries covered alternate layers of decayed plant organisms, until finally beds of peat were formed. Great masses above pressed on those underneath; the internal heat of the earth reached up and transformed the densely packed masses of peat until the beds became hard and brown, the product of the partial metamorphism being what we know as lignite, or brown coal. With the continued action of the forces of metamorphism, the lignite turned still darker, and as more gases were driven off, became heavier, until the bituminous stage was reached, which, in turn, was succeeded by the anthracite stage.