THE MAMMOTH.
This is the great bed of the anthracite coal-fields, and perhaps, considering its extent and frequent enlargements, the most magnificent coal-bed in the world. Its most pro ductive or best condition is perhaps thirty feet in thick ness; but it varies from 12 to 70 feet. In figure 81 we have given it as 25, which may be accepted as its average size in this district. In the Lehigh district it ranges from 40 to 60, but contains less workable coal than it does when only 30 feet thick, as in the Lehigh detached basins and elsewhere. In the New Boston basin it is over 60 feet thick, vertically across the strata of the coal, while the bed is uniformly deposited in a moderately dipping basin. Generally, those great enlargements are on an axis of formation, either synclinal or anticlinal, where the vein is doubled, and, consequently, the benches are counted twice. But in the New Boston basin such is not the case. The vein is evenly stratified and single. In the Mahanoy region the average size of the Mammoth is from 25 to 30 feet in thickness ; but there, as elsewhere, several great enlargements are found. One of these is at the McNeal col liery, where the vein is over 50 feet thick, and another is at. Shenandoah City, where it is between 70 and 80 feet thick. But both these excessive dimensions are on.the vertical north dips, where the vein is probably doubled. In the Shamokin region the Mammoth is divided, and is known as the Twin veins. Each division ranges from 9 to 16 feet in thickness, and is divided by from 10 to 40 feet of slate and sandstone. In the Lehigh basins its size is generally uniform, and ranges from 25 to 35 feet, and the bed is in fine condition.
In the Wilkesbarre district of the Northern coal-field, the Mammoth, under the name of the Baltimore vein, is about 20 feet thick ; in the Pittston district about 12, and the Scranton 14 feet. At Carbondale it is 20 feet thick ; but there it is composed of several of the accompanying veins, brought together by the thinning of the strata in that direction.
A peculiar and favorable feature of the Mammoth is its massive and solid benches of pure coal, which frequently exceed four feet without a streak of bone or impurity, and often from ten to twelve feet without any marked parting of bone or slate to denote a change or interval in the pro cess of formation. We cannot conceive any possible or probable process by which these masses of coal could have been formed by arborescent vege tation. It is simply impossible. We are forced, therefore, to more natural conclusions, or such as we discussed pretty fully in the opening chapters.
The Mammoth vein now produces over two-thirds of all the anthracite coal mined ; and perhaps we might increase the amount without over-esti mating it. As long as the Mammoth bed is productive at moderate depths, the smaller seams will remain in statu quo. The difference in the cost of mining coal from those large white-ash beds or from the small red-ash seams cannot be less than 50 per cent., and, including risk from faults and irregularities, perhaps much more. The Mammoth is the most regular and reliable of all our veins, the most economical to mine and operate, and, from its size, the most productive.
The "SEVEN-FOOT VEIN" is a leader or satellite of the Mammoth. It is generally persistent throughout the Pottsville district, and usually found in the Mahanoy region; but generally in other sections it is combined with the Mammoth. Its size varies from 4 to 10 feet, and its character is generally rather coarse and bony. We do not consider it a regular bed, for the reasons before mentioned. Its distance above the Mammoth varies from 0 to 20 feet. The latter is its usual position in the Pottsville and Mahanoy districts.
The identity of the anthracite with the bituminous coal-beds can no doubt be made ; but we do not think our miners and mining engineers have begun right, nor do we think it possible to identify them if the Pittsburg seam is taken as cotemporaneous, or on the same horizon with the Mammoth, for reasons which we may briefly explain.