ings is well illustrated by the sections of the Mammoth bed shown by page plate No. 3.

If we consider only the very thick beds in estimating the amount of refuse, the percentage above mentioned is apparently much too small. In the Mammoth and other large beds. from one fourth to one half the total thickness frequently consists of refuse.

Thus the sections shown on Page Plate No. 3, give:

In the forthcoming geological report illustrations will be given of seams splitting into two, three or more well-defined beds, by a simple swelling of these parting bands. That this feature is not peculiar to the anthracite is proven by similar instances recorded in the Geology of Yorkshire,* (England,) and in reports V, and VV, of the Pennsylvania survey and in other publications.

The partings found in anthracite beds are, as a rule, much harder than those occurring in bituminous seams-hence the difficulty experienced in attempting to mine anthracite by "bearing in" on a slate parting (underholing) after the fashion of bituminous mining.

Roof. The roof of anthracite coal beds is usually a dark slate, hard and tough, sometimes, however, soft and shaly, or sandstone or conglomerate. A sandstone or "rock roof” or a hard firm slate roof furnishes an excellent mining cover; but the soft carbonaceous slates and irregularly bedded shales are very treacherous.

Floor. The character of the floor is not usually of much consequence except at mines working on very steep pitching beds. It is generally hard and firm, sometimes an indurated fire-clay but sometimes slate and occasionally sandstone. The soft fire-clays occurring in the bituminous region are almost unknown in our anthracite mines.

* Geological Survey of England and Wales, 1880.

The place of anthracite among fossil fuels.

All the fossil fuels known as coal, lignite, peat, and by other names consist of variable proportions of carbon, and volatile hydrocarbons, with a small percentage of water and a variable amount of accidental impurities.

In classifying the different varieties of coal, the impurities-water, sulphur, phosphorus, and the earthy salts constituting the ash-may be ignored, for the presence of these is accidental, and, although they greatly diminish the value of a coal when present in large amount, they do not appreciably affect the composition of the coal as fuel.

In other words, two coals containing the same relative amounts of fixed carbon and volatile hydrocarbons, should theoretically be classed together, without reference to their relative percentages of impurities.

This method of classification, devised by Prof. Walker R. Johnson, and adopted in his report on "American Coals," 1844, has recently been ably discussed in a paper by Prof. Persifor Frazer, which, with a lengthy analysis by Prof. J. P. Lesley, and annotations by Mr. A. S. McCreath, was published in the Report of Progress in the Laboratory of the Survey, (MM,) 1879.

The percentage of fixed carbon to volatile hydrocarbons may vary between the two limits 100: 0 and 0: 100, but neither the first, represented by graphite and the diamond, nor the second, represented by some of the purer petroleums, can be classed as coal. The coals fall between these limits.

Professor Frazer has suggested that the lines of division between coals of the different classes be drawn as follows:

The commercial distinction between anthracite, semi-anthracite, semi-bituminous, and bituminous coals is largely governed by the geographical location of the mines from

which the coal is obtained, and it thus often happens that a coal sold as semi-anthracite, because it is mined in or near a certain locality, really has a higher fuel-ratio (amount of carbon to volatile hydrocarbons) than another coal sold as hard-dry anthracite because it comes from such an anthracite district. It will be impossible to break down these arbitrary commercial divisions; but even if feasible, would it be advantageous? At present the buyer knows the coal he is using by its local or trade name; under the new classification he might think to get the same coal when ordering from the same class,-i. e., coal with the same fuel ratio,but might not be pleased with differences in physical character and in the percentage of sulphur and ash.

The following rough generalization may be useful, but its utility is limited by the fact that the coals of each class, as known to the trade, overlap into those both above and below it:

In coals known as

Anthracite, .. Volatile matter is usually less than 7%. Semi-anthracite,. Volatile matter is usually less than 10%. Semi-bituminous, Volatile matter is usually less than 18%. Bituminous, .. Volatile matter is usually more than 18%.

The different varieties of semi-bituminous and bituminous coals are thus grouped and described by Prof. Rogers: Semi-bituminous Cherry Coal. Semi-bituminous Splint Coal.

Semi-bituminous

Bituminous

{

Coking Coal.

Cherry Coal.

Splint Coal.

Anthracite coal is characterized by its small percentage of volatile matter, high specific gravity, hardness, nearly metallic luster, rich black color, and semi-conchoidal fracture. It ignites with difficulty, produces an intensely hot fire, giving off no smoke, and burns with a very small blue flame of carbonic oxide (produced by incomplete combustion), which disappears after the coal is thoroughly ignited. Semi-anthracite coal is neither as hard nor as dense as anthracite, its luster not so brilliant; its percentage of vol

atile matter is greater, and the cleavage planes or "cleats" are much closer, the fracture often approaching the cuboidal.

Semi-anthracite coal is confined principally to the western ends of the anthracite basins, as at Shamokin, etc.

This coal when ignited burns at first with a flame somewhat resembling that of the bituminous coals; but this shortly ceases, and the anthracitic character of the coal becomes at once apparent.

Cherry coal is a deep black, dull or lustrous coal, with a somewhat conchoidal fracture, readily breaking up into cuboidal fragments. It ignites easily, making a hot, quick fire, with a yellowish flame, and retains its shape until thoroughly consumed. Its specific gravity is much less than anthracite, about 1.30.

Splint coal is of nearly the same specific gravity as cherry coal, which it somewhat resembles. It has a slaty longitudinal and a very uncertain cross fracture. It is not very easily kindled, and makes a slow, dull fire.

Cherry and splint coal, of both the bituminous and semi-bituminous varieties, usually leave a rather large percentage of ash.

Cannel coal is remarkable for its dull, slaty, or resinous luster, its conchoidal or slaty fracture, and its large percentage of volatile hydrocarbons. It burns with a long flame, giving off a large amount of smoke, and usually leaves a very large percentage of ashes.

Caking or coking coal, the most important of the bituminous coals, is readily known by its behavior in the fire. It burns with a long yellow flame, giving off more or less smoke, and creates an intense heat when properly attended. It is usually quite soft, and does not bear handling well. In the fire it swells, fuses, and finally runs together in large masses, which are rendered more or less porous by the evolution of the contained gaseous hydrocarbons. The cleat and cleavage joints (butt and face) usually run nearly at right angles, giving the coal a cubical fracture.