Page:The American Cyclopædia (1879) Volume I.djvu/586

 550 fields and connect- ed with the bitu- minous coal beds of the Alleghany field, designates the lowest work- able and consistent bed as A and the highest as K But this nomenclature denotes series or groups of coal beds, rather than single beds. Fig. 1 presents the gen- eral type of the Pennsylvania an- thracite strata. The figures in the column and in con- nection with the letters indicate thickness in feet. A number of small unworkable seams are not here repre- sented. The 15 groups from A to N include 30 beds above 2 ft. thick and 20 seams less than 2 ft. This mode of grouping the beds in the an- thracite fields was suggested by the natural divisions of massive sand- stone and con- glomerate strata in the coal meas- ures, and the fre- quency with which some of the promi- nent groups united as a single bed or divided into two or three beds. In the southern an- thracite field of Pennsylvania a few imperfect, ir- regular, and im- pure "nests" or pockets, rather than beds, of graphitic anthra- cite are occasion- ally found below A ; but these local deposits have no general horizon, and are valueless for commercial purposes. Though .pockets of good ANTHKACITE I'J 13 14 15 --* 10 B 10 FIG. 1. AMTHEACITB STRATA coal are sometimes found from 5 to 20 ft. thick, they vary to as many inches, and do not exist as regular and consistent beds. A is usually a small bed of red-ash coal, but two or three thin seams are frequently found in this group which exist in the conglomerate, or close to it, every- where. The coals of A generally contain from i 10 to 20 per cent, of earthy matter, and are sel- dom workable. B is generally a large bed from 10 to 30 ft. thick, but frequently two beds of 5 to 10 ft. each. The lower part produces red- ash coal, and the upper gray or pink. The coal is excellent, and valued for blast furnances, though it contains more silica than the coal of any other workable bed higher in the measures. C is usually a group of small unworkable beds, producing white or gray-ash coals. D is a single bed of pure white-ash coal, generally from 6 to 10 ft. thick. E is the celebrated mammoth, which is a single bed from 20 to 70 it. thick in some localities, and a group of two and three in others. The coal is always of the white-ash variety, and is hard, dense, pure, and lustrous. Fully eight tenths of the present anthracite production is from this group. F is composed of two small beds of white-ash coal, and is not of much value; it is often known as the " rough vein." G is generally a large bed from 7 to 10 ft. thick, and always a single one, though the lower stratum produces white-ash and the upper pink or gray-ash. It is locally known as the gray-ash or primrose vein, and is supposed to be identical with the Pittsburgh bed in the bituminous field. All the workable beds, from A to G inclusive, pro- duce blast furnace coal ; but the coals of the beds from G to N are less dense and contain less carbon and more volatile matter than the lower coals, and crumble under a high temper- ature. They are therefore not used for steam and furnace purposes generally, but are much valued for household uses, excepting large fur- nace heaters. They evolve an intense heat, and are free-burning, but will often " clinker " un- der a strong draught. In the preceding analyt- ical table the highest percentage of carbon is 94-10 (No. 6), which is a hand specimen from the mammoth bed, E, in the Pottsville district ; but it is a well known fact that the mammoth coals of the Lehigh district are equally as pure and generally more dense than any other an- thracite. The average, therefore, of Nos. 1, 2, i 3, 4, and 6 will give the mean of the hardest and purest anthracite ; while No. 6 (M) is a type of the upper coals, and approaches the limit of the true anthracite, as shown by 7 and 8, which are semi-anthracite and semi-bitumi- nous. The density and hardness of the coal de- i crease from A to N in the ascending order, while the volatile matter increases from N to A in the descending order ; and the proportions of carbon increase and decrease in the same ratio and order. The coals of the lower beds are most hard and dense. The middle beds pro- duce the purest coal, and the coal of the upper beds is most soft and friable under heat. The