occur in the same group of strata, represent ancient beds of calcareous marls. The slow progression of these changes is indicated by the different ages of the geological formations in which the several varieties occur. Beds of peat are of recent formation, though some of them are still so old, that they are found at different depths, one below another, separated by intervening layers of sand, clay, and earth. Brown coal, or lignite, is commonly included among the strata of the tertiary period; the bituminous coals are in the secondary formations; and the anthracites, though contained in the same geological group with the great bituminous coal formation, are in localities where the strata have all been subjected to the action of powerful agents which have more or less metamorphosed them and expelled the volatile bitumen from the coal. The graphite or plumbago is in still older groups, or in those which have been still more metamorphosed by heat.

oxygen, and the little nitrogen in their composition, may be distributed in the forms of carburetted hydrogen,, ammonia, the bituminous oils, etc., cannot be ascertained by analysis, as the means employed to separate most of these compounds cause their elements to form other combinations among themselves: the determination of the ultimate proportions of all the elements would serve no practical purpose. So, if it be required to prove the fitness of any coal for affording illuminating gas, or the coal oils, it must be submitted to experiments having such objects only in view; and even their capacity for generating heat is better determined by comparative experiments in evaporating water, than by any other mode. The bituminous coals are characterized by their large proportion of volatile matter, which, when they are heated, is expelled in various inflammable compounds, that take fire and burn, accompanied by a dense, black smoke and a peculiar odor known as bituminous. All these varieties of fossil fuel are found If the operation is conducted without access in the United States. Peat beds of small of air, as in a closed platinum crucible, the extent are common in the northern portion fixed carbon remains behind in the form of of the country, and in some parts of New coke; and by removing the cover to admit England are much used for fuel, and the air, this may next be consumed, and the remuck, or decomposed peat, as a fertilizer to siduum of ash be obtained. By several the soil. In the great swamps of southern weighings the proportions are indicated. Virginia, the Carolinas, and Georgia, vegeta- Coals containing 18 per cent. or more of ble deposits of similar nature are found upon volatile matter are classed among the bia scale more commensurate with the extent tuminous varieties; but as the proportion of of the ancient coal-beds. Lignite is not this may amount to 70 per cent. or more, found in workable beds, as in some parts of there is necessarily a considerable difference Germany and England, but in scattered de- in the characters of these coals, though their posits of small extent among the tertiary most marked peculiarities are not always clays, chiefly near the coast of New Jersey, owing to the different amounts of volatile Delaware, and Maryland, and in the west- matter they contain. Thus, some sorts, called ern territories. The distribution of the true the "fat bituminous," and "caking coals," coal formations will be pointed out after des- that melt and run together in burning, and ignating more particularly the characters of are especially suitable for making coke, conthe different coals All of these consist of tain about the same proportion of volatile the elements carbon, hydrogen, oxygen, and matter with the "dry coals," as some of the nitrogen; the carbon being in part free, cannel and other varieties, which burn withand in part combined with the other ele- out melting, and do not make good coke. ments to form the volatile compounds that Other varieties are especially distinguished exist to some extent in all coals. Earthy for their large proportion of volatile ingrematters which form the ash of coals are al- dients; such are the best cannels, and those ways intermixed in some proportion with light coals which have sometimes been misthe combustible ingredients, and water, also, taken for asphaltum, as the Albert coal of is present. When coals are analyzed for the province of New Brunswick. These vathe purpose of indicating their heating qual-rieties are eminently qualified for producing ity by their composition, it is enough to de- gas or the coal oils; but have little fixed cartermine the proportions of fixed carbon, of bon, and consequently can produce little volatile matter, and of ash which they con- coke. Coals that contain from 11 to 18 per tain. How the combined carbon, hydrogen, cent. volatile matter, are known as semi-bi

tuminous, and partake both of the qualities of the true bituminous coals, in igniting and burning freely, and of the anthracite in the condensed and long-continued heat they produce. The Maryland coals, and the Lykens valley coal of Pennsylvania, are of this character. The true anthracites contain from 2 to 6 per cent. of gaseous matters, which by heat are evolved in carburetted hydrogen and water, even when the coal has been first freed from the water mechanically held. Their greatest proportion of solid carbon is about 95 per cent. There remains a class which has been designated as semi-anthracite, containing from 6 to 11 per cent. of combustible volatile matter. These coals burn with a yellowish flame, until the gas derived from the combination of its elements is consumed.

others it is gray, as in the Lehigh coals. This distinction is used to designate some of the varieties of anthracite; but the quality of these coals is more dependent on the quantity of the ash, than on its color. From numerous analyses of the Schuylkill red ash coals an average of 7.29 per cent. of ash was obtained, and of the white ash anthracite, 4.62 per cent. Coals producing red ash are more likely to clinker in burning than those containing an equal amount of white ash. In some varieties of coal the proportion of earthy matter is so great that the substance approaches the character of the bituminous shales, and may be called indifferently either shale or coal. Though such materials make but poor fuel, some of them have proved very valuable from the large amount of gas and of oily matters they afford. The The earthy ingredients in coals, forming most remarkable of this class is that known their ash, are derived from the original wood as the Boghead cannel. This is largely and from foreign substances introduced mined near Glasgow, in Scotland, and is imamong the collections of ligneous matters ported into New York to be used in the that make up the coal-beds. The ash manufacture of coal oil. It is a dull black, is unimportant, excepting as the material stony-looking substance, having little resemwhich produces it takes the place of so much blance to the ordinary kinds of coal. Its combustible matter. In some coals, espec- composition is given for comparison with ially those of the Schuylkill region, it is red, that of other coals, in the following tafrom the presence of oxide of iron, and in ble :

Localities.

Shenowith Vein, Penn...

Peach Mountain, Penn.; mean of 40 analyses.... W. R. Johnson.. 1.46

.H. D. Rogers....... 1.50

A complete description of the coals, such steam quickly; 2, for raising it abundantly as may be found in the Report of Prof. for the quantity used; 3, freedom from Walter R. Johnson (Senate Document, 28th dense smoke in their combustion; 4, freedom Congress, No. 386), and presented, in a from tendency to crumble in handling; 5, condensed form, in Johnson's Edition of capacity, by reason of their density, and the "Knapp's Chemical Technology," presents shapes assumed by their fragments, of close many other features affecting the qualities stowage; and 6, freedom from sulphur. The of the coals, and their adaptation to special last is an important consideration, affecting Such are 1, their capacity for raising the value of coals proposed for use in the

uses.

iron manufacture, sulphur, which is often yards and on board ships have been thus present in coal in the form of sulphuret of inflamed, involving the most disastrous coniron, having a very injurious effect upon the sequences. In stowage capacity coals difiron with which it is brought in contact fer greatly, and this should be attended to when heated. It is again to be cautiously in selecting them for use in long voyages. guarded against in selecting bituminous Tendency to crumble involves waste. Dense coals to be employed in steam navigation; smoke in consuming is objectionable in coals for by the heat generated by spontaneous required for vessels-of-war in actual service, decomposition of the iron pyrites, the eas- as it must expose their position when it may ily ignited bituminous coals may be readily be important to conceal it. The following set on fire. This phenomenon is of frequent table was prepared by Prof. Johnson to preoccurrence in the waste heaps about coal sent some of the general results in these mines, and large bodies of coal stored in particulars of his experiments :

GENERAL SCALE OF RELATIVE VALUES FORMED FROM THE AVERAGES OF EACH CLASS OF COAL

Column 1 gives the relative evaporative powers of equal weights of the coals; 2, the same of equal bulks; 3, their relative freedom from tendency to clinker; 4, rapidity of action in evaporating water; 5, facility of ignition, or readiness with which steam is gotten up. The general results of experience in use, as well as of special trials systematically conducted upon a large scale, agree in these particulars-that while the bituminous coals are valuable for the greater variety of uses to which they are applicable, and especially for all purposes requiring flame and a diffusive heat, as under large boilers; and while they are quickly brought into a state of combustion, rendering the heat they produce more readily available; the anthracites afford a more condensed and lasting heat, and are to be preferred in many metallurgical operations, especially where great intensity of temperature is required. And for many purposes, the free-burning, semi-bituminous coals, which combine the useful properties of both varieties, are found most economical in use.

the various members of its formation, its fossil organic remains, its mineral accompaniments, and by its position relative to the other groups of rock which overlic and underlie it. The principal one of these fields or basins is that known as the Appalachian, which, commencing in the north-eastern part of Pennsylvania, stretches over nearly all the state west of the main Alleghany ridge, and takes in the eastern portion of Ohio, parts of Maryland, Virginia, Kentucky, Tennessee, the north-west corner of Georgia, and extends into Alabama as far as Tuscaloosa. Its total area, including a number of neighboring basins, as those of the anthracite region to the east of the Alleghany ridge, which were originally a part of the same great field, is estimated at about 70,000 square miles. A second great basin is that which includes the larger part of Illinois, and the western portion of Indiana and of Kentucky. Its area is estimated at about 50,000 square miles; the coal is bituminous, and largely charged with oil.

The third coal field, now known as the Rocky Mountain Coal Field, is the largest in the world, embracing an area in North America of 1,250,000 square miles of which 513,000 square miles is within the United States. It covers large areas in Texas, the Indian Territory, New Mexico, Kansas, Nebraska, Iowa, Dakota, Montana, Wyoming, and Colorado. The coal is semi-bituminous and of good quality. The coal of the Pacific States is mainly lignite, containing about 50 per cent. of carbon, but on Vancouver's