COAL. This highly important sub stance is found in beds or strata in that group of the secondary rocks which in cludes the red sandstone and mountain limestone formations and which is com monly called the carboniferous group, or coal measures. From the peculiarities of their depositions they are often spoken of under the names of coal basins, and coal fields. There are two or three points, and those of much theoretical importance, respecting the origin of coal, on which geological authorities are nearly unani mous. The one is, that our present coal is exclusively of vegetable origin, formed apparently from the destruction of vast forests ; and the prodigious quantities of timber drifted by some of the great rivers of the world into the present ocean render it not improbable that a similar formation may now be carrying on in the depths of certain parts of the sea. Secondly, from the nature of the preserved vegetables it appears probable that the climate of these parts was not merely tropical, but ultratropical. It may also be inferred that the coal strata were deposited in the neighborhood, and often probably upon the very verge of exten sive tracts of dry land ; for the trees that are found in coal strata are often like those of our submarine forests, as far as position goes. And, finally, the deposits of coal appear afterwards to have been elevated, and often singularly dislocated and contorted by forces acting from be low, and probably of a volcanic nature. In some coal fields there are appear ances which justify the term coal basin : they are of limited extent, frequently dip as it were to a common centre, and con sist of various beds of sandstone, shale, and coal, irregularly stratified ; and sometimes mixed with conglomerates, showing a mechanical origin.
That these deposites have taken place, and that the change of wood into coal has often been effected under great pres sure, and often under the pressure of heat, seems evident from the appearance of some of the vegetable masses, and al so from the manner in which the carbu retted hydrogen escapes in the form of blowers and eructations from the strata, as if pent up in their cavities under vast condensation, and even sometimes, per haps, in a liquid form.
Though there are often many beds and seams of coal in one field, it is seldom that many of them are worked. They are generally of uniform thickness through a great extent, but are some times subject to irregularities. When less than two feet thick they are sel dom worked to any great extent. The nature of the upper stratum, or stony matter of the roof, is very important : rf compact, it is secure from falling, and keeps out water ; if loose, the expenses incurred in supporting it absorbs the profits of the coal.
The Beds of Coal in the U. S. are numer ous and extensive, embracing the whole country from the border of New Bruns wick to Tuscaloosa in Alabama, and from the Alleghenies to Vancouver's Island.
The coal is of both kinds, anthracitic and bituminous. The former existing on the slope of the Alleghenies, where, by up heaval of heated mineral masses, the bitu men has been expelled, and the coal con verted into anthracite. The bitumen in coal increases as the beds pass westward toward the Mississippi, where as well as on the Pacific shores, the quantity of bitumen is equal to that in English sea coal. The geological survey of the state of New York has not brought to light any important deposit of coal in that state ; but it has been stated in the Al bany Evening Journal of 1850, that a seam of coal, four feet in thickness, has been discovered by Mr. J. N. Cutler, of that city, in Coeymans—a few miles only from Albany, on the farm of a Mr. Vanduzee. It is believed to extend through Albany, Green, and Schoharie counties.
The three great coal-fields in the country are :—the Ohio, 740 miles long, and 180 wide, covering an area of 60,000 square miles ; the Illinois coal-field, covering 50,000 square miles ; and the Michigan, 15,000 square miles. Besides these, there are the numerous anthracitic basins in Pennsylvania and Virginia, the furthest being 100 miles S.E. of the margin of the Ohio coal-field. In passing across the coal-fields there is a gradual diminution of the bitumen eastward. The coal of every kind rests on the same basis of rock, with the same fossils distributed through it, and the particular coal-fields can be identified even when separated by an interval of 50 miles. The anthra cite field is 5000 feet deep, and contains 50 seams of coal. The bituminous coal field of Ohio is 2,800 feet deep, 8,000,000 tons of anthracite, and 1,000,000 tons of bituminous coal are raised yearly. The anthracite coal-mines on the Lehigh River, Pa., are worked like an open quar ry on the slope of a mountain, rising 900 feet above the river. The coal is 60 feet thick, and surrounds the quarry in black glistening walls, capped by 40 feet of yel low sandstone, and is conveyed by a self acting railway for eight miles down a de clivity, from 100 to 140 feet per mile, the whole of obtaining being about 4 cents a ton ; when quarried to some distance the bed splits up into branches. The anthra cite district extends across two counties, Luzerne and Schuylkill. At Portsmouth, R. I., a bed of anthracite has been worked for 25 years back. A mine of anthracite has been open in Worcester, Mass., at the head of the Blackstone Canal. The cost of transport of a ton of coal is— From haunch Chunk to Philadelphia $1 93 From Staunch Chunk to New York . 2 42 From Penhatn to Philadelphia . . 1 93 From Penham to New York . . 2 55 The value of coal exported in 1850 was $167,090. The coal imported in the same year was 180,439 tons, value $378,817.