Fig. 34.—Map showing the distribution of coal in North America.
The coal-fields of North America are more extensive than those of any other continent, excepting, perhaps, the at present but little known coal-bearing formations of Asia, and are distributed in temperate latitudes, from tide-water on the Atlantic to tide-water on the Pacific coasts, where the greatest commercial and intellectual development has been reached.
Coal of Carboniferous age occurs in large and valuable deposits in Nova Scotia and New Brunswick; there is a small area of graphitic anthracite, not now utilized, in Rhode Island; but the great fields are in Pennsylvania and the States southward to central Alabama, and westward to beyond the Mississippi. A detached coal-basin containing some 6,700 square miles, but a small part of which is productive, however, occurs in the central part of southern Michigan. Small coal-fields in Virginia and North Carolina, the first to be worked in America, are of Jura-Trias age and form part of the Newark system. Extensive fields of valuable coal of Mesozoic age, principally in the Laramie system, occur in New Mexico, Colorado, Wyoming, Montana, and still farther north along the same great belt in Canada.
Another highly valuable field of Mesozoic coal is now being extensively worked on Vancouver Island. The
coals of the west side of the Pacific mountains, largely lignites, but in many instances of high grade and serviceable for steam coal, are mostly of Cenozoic age (Tertiary) and occur in California, Oregon, Washington, and Alaska. The distribution of the various coal-fields is indicated on the above map, and space will not be taken in describing their geographical relations.
Peat is present in innumerable swamps throughout the humid, temperate portion of the continent, especially from Louisiana and Florida northward, to the region about the Great Lakes and widely throughout Canada, but is at present of small commercial importance, although steps are being taken for its extensive utilization.
The most valuable of the coal deposits are of Carboniferous age, and lie to the east of the Rocky Mountains. The most of the coal is bituminous, or soft coal, used principally in generating steam and for manufacturing gas and coke. The exceptions occur in eastern Pennsylvania and in Rhode Island. These are considered as metamorphosed coals, although in the Pennsylvania region there is no evidence of the action of a high degree of heat. In the Rhode Island field the rocks associated with the coal are plainly metamorphic in character, and the coal has, in large part, been changed to graphitic anthracite.
That anthracite may be of any age, however, is indicated by the local changes that have occurred in Mesozoic and Cenozoic coals, where they have been penetrated by dikes and other varieties of intrusions, or have been altered by surface lava-flows. In such situations the coal has lost nearly all its volatile matter, and in composition and in certain instances, as in western Colorado, in physical character as well, is essentially an anthracite.
In addition to the various coal deposits referred to above there is a second series of organic compounds found stored in sedimentary rocks which consists of hydrocarbon. This series of substances includes natural or rock-gas, petroleum, maltha or semifluid hydrocarbon, and solid hydrocarbons, such as asphaltum, albertite, grahamite,