COAL
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COAL
the accumulated vegetation compressed it into more and more compact form. As the result of the chemical changes and the compression, the vegetable matter was gradually brought to the condition of coal.
In many regions there are numerous seams or beds of coal, one above another, separated by beds of shale, sandstone, etc. Each bed of coal represents the succession of conditions sketched above. After the burial of one body of vegetable matter the area was perhaps elevated sufficiently to cause it to become a marsh again, and the growth of vegetation followed. This in turn was buried.
Wood contains about 50 per cent, of carbon. In the chemical changes which it undergoes in peat-bogs, it loses some of the carbon, but still more of its oxygen and hydrogen, so that the proportion of carbon remaining after the changes is greater than before. Peat contains about 60 per cent, of carbon. With the loss of more hydrogen and oxygen, and with compression which renders it solid, peat is transformed into coal When the changes have gone so far that the proportion of carbon is as great as 90 per cent., the coal is anthracite. When the proportion of carbon is less, the coal is said to be bituminous or soft. Of bituminous coal there are many grades, depending partly upon the proportion of carbon. The chemical changes in the vegetable matter may go so far that the proportion of volatile matter (hydrogen and oxygen) is reduced to one or two per cent. In this condition the coal is said to be graphitic. Graphitic coal does not burn readily. Anthracite coal, which contains relatively little volatile matter, burns with little flame. Bituminous coal, which contains more volatile matter, burns with flame, and in general burns more readily as the proportion of volatile matter increases. There are several varieties of bituminous coal, named according to their uses. Among them are coking-coal, furnace-coal, cannel-coal, etc. Coking-coal melts on becoming hot, and after the volatile matter escapes the solid product is coke. It has much the composition of anthracite coal, but is spongy in texture. Cannel-coal is impure, and contains much volatile matter. It is rather earthy in texture, and less hard than most other varieties of coal. It is extensively used for burning in grates Furnace-coal is any sort of bituminous coal appropriate for use in furnaces.
Anthracite coal occurs mainly in regions of folded strata, where the folds have been greatly eroded. The compression to which the coal was subject in the process of folding, the heat generated by the compression and the subsequent exposure of the coal-beds after erosion, allowing the volatile matter to escape, have probably been the
chief factors in the transformation of soft coal into anthracite. In some places in New Mexico and Colorado soft coal has been changed into anthracite by contact with lava. Bituminous coal, as may be inferred from the above, usually occurs in regions where the strata are horizontal or but slightly tilted.
The coal of the United States belongs partly to the carboniferous system (see GEOLOGY) and partly to the systems of later periods, especially to the last part of the cretaceous. There is a little coal in the triassic system of the east (Virginia and North Carolina), and very considerable quantities of coal in the tertiary of the west, especially in Washington.
The coal product of the leading coal producing countries in 1910 was as follows:
United States........... 501,596,378 metric ton
Great Britain........... 296,007,699
Germany............... 245,043,120
Austro-Htmgary (1909) • • 54.573,788
France................. 42,516,232
Belgium................ 26,374,986
Russia and Finland...... 24,967,095
Japan (1909)............ 16,505,418
The total product of all other countries was probably not more than 40,000,000 tons.
The United States coal-fields of the carboniferous period are as follows:
1. New England field (Rhode Island and Massachusetts—coal more or less graphitic and little used).
2. The Appalachian coal-field, including the coal-producing areas of Pennsylvania, eastern Ohio, Maryland, Virginia, West-Virginia, eastern Kentucky and Tennessee, Georgia and Alabama; area, 58,695 square miles.
3. Northern coal-field, part of southern Michigan, 6,700 square miles.
4. The central coal-fields, including the coal-producing areas of Indiana, Illinois and western Kentucky, 47,250 square miles.
5. The western coal-field, including the coal-producing areas of Iowa, Missouri, Nebraska, Kansas, Arkansas, Oklahoma and Texas, 98,700 square miles.
Coal-formations of cretaceous age occur in Dakota, Montana, Wyoming, Utah, Colorado and New Mexico. Coal-formations of tertiary age occur in Washington, Oregon, California and Alaska, but especially in Washington, where the amount of coal is large. The area of the cretaceous coalfields is probably as great as that of the carboniferous coal-fields. The area of the tertiary coal-fields is not known. The amount of coal in these western fields has not been estimated. It perhaps equals that in the carboniferous system, though the quality of the coal is on the whole inferior.
The anthracite coal of the United States is derived chiefly from Pennsylvania. Colorado and New Mexico, however, produce some. Pennsylvania also leads in the pro-
