SOUTH WALE'S ANTHRACITE COAL.
We have, perhaps, devoted more space to the Newcastle coals than would be prudent if we proposed a general description of the English coal-fields in detail; but such a course would be neither appropriate nor desirable in a work essentially American and devoted to an exposition of our mineral resources.
We have dwelt at more length on the Great Northern coal-field than we shall on any other British or foreign coal-field, because it has an historical interest and stands first in the annals of the coal-trade, as it is first in pro duction, importance, and development. We shall now glance briefly at some of the peculiar English coal-formations, which may possess more than ordinary interest to the general reader, and simply refer to others, before dismissing the subject for the present. Under the heads of ventila tion and economic milling, we shall again have occasion to cite the examples of British mines and miners.
The South Wales coal-field lies on the northwest of the Bristol Channel, extending from St. Bride's Bay in the east to Pontypool in the west, a distance of 90 miles, with a maximum breadth of 60 miles. Its mean breadth is less than 20 miles ; presenting a productive coal area of from 1000 to 1500 square miles. It is divided longitudinally by an axis parallel to its strike, and divided also into numerous intermediate basins, while the measures undulate both from east to west, and from north to south, though the representations of the field, across the axis from north to south, are generally in the form of two immense basins, as portrayed by our transverse section above.
The deepest part of the field is supposed to be 8000 feet; that is, through the coal measures to the conglomerate. The depth of this field has been stated as 12,000 feet; but this statement includes some of the rocks below the coal, such as the millstone grit and the Carboniferous limestone. Most of the mining has been done by drifts, to the present date, and but few shafts have been. sunk to any great depth.
Twenty-three workable seams exist in the principal basins, averaging altogether 92 feet of coal: of these, 12 are from 3 to 9 feet in thickness, and 11 from 13 inches to 3 feet. Besides these, there are numerous smaller seams from 6 inahes to 18 inches thick.
On the north side of the field the coal is anthracite in character, and resembles the anthracites of Pennsylvania, though generally containing more hydrogen or volatile matter ; on the east, or northeast, the coal is semi-biturainous, and is used extensively, both raw and coked, in the blast-furnaces of the region.
On the south side the coal is of a bituminous character. The change from anthracite to semi-bituminous and bituminous is gradual, and much the same in its metamorphic phases as we find existing in the coal-fields of Pennsylvania. As a pure anthracite it is used raw, but with hot blast in the furnace; but as a semi-anthracite it can be used raw with cold blast; and it is stated that the best pig-iron made with mineral fuel in Wales is produced with raw anthracite and cold blast. As a semi-bituminous coal, it is coked generally before use in the furnace, but even this coal is frequently mixed, both raw and " coked anthracite" being used in the furnace together.
There are 16 thin seams of iron-stone interstratified with the coal ; the general yield of this ore is not over 30 per cent. of metal in the furnace; but being carefully calcined, and both coal and ore being pro duced on the spot, at low prices, iron can be manufactured as cheap at the Great Dowlias, or Merthyr Works, as in any part of the world.
The iron-masters of Wales discover, however, that a certain percentage of the richer ores, even at a much higher cost, not only improves the make, but reduces the general cost.
The coal production of South Wales in 1854 was 8,550,270 tons : of this amount, only 1,000,000 tons were anthracite,—the total being the products of 245 collieries.
The analysis of South Wales coal shows a larger amount of bitumen than coals of the same name in Pennsylvania.
We do not consider, however, that much dependence can be placed on such analytical tables as we possess; they are generally compiled from a variety of sources, and are, therefore, not entitled to credence. The Eng lish and French chemists always produce a closer analysis than ours have done, as a rule. The coals tested by Clemson, Johnson, Jackson, and other American chemists, always produce, as a result, from 2 to 10 per cent. more residue than the same coals when analyzed by Mushet or Berthier. There is, also, much difference in the results obtained by individuals. The same samples of coal, analyzed by three or four different persons, would show widely different results. Therefore, unless we have a series of analytical tests by one competent person, but little dependence can be placed on our tables of the constituents of coal for practical purposes.