Coal seam

“ It holds three coal seams of 2 feet 6 inches, and 5 feet and 5 feet respectively. [Pg 141] There is not much evidence of fracture in any part of the field. The total thickness of the coal-bearing rocks is estimated by Bailey Willis to be 1,000 feet. This is evidently the lower part of the coal series, the upper part having been carried away. The best seam is mined at Roslyn, four miles north of the Northern Pacific Railroad, in the interest of that railroad.
The seam here furnishes upward of four feet of good coal. The coal is bituminous, dull black, firm, and free burning. ”

“ Good coal.This is a good seam of coal, five feet six inches of which can be depended on for shipping. The coal is dull-black in color, and easily mined. The bottom is soft sandstone. Overlying the roof-slate, is sandstone. The seam here is said to be one foot thicker than it is at Newcastle.
COAL-BUNKERS OF THE SEATTLE, LAKE SHORE AND EASTERN RAILWAY, ON SEATTLE HARBOR.
Another good coal seam.Seam No. 2 has been uncovered by the diggings on the railroad, and happens to be at an unfortunate place for showing the coal. ”

“ In opening a coal mine on a hillside, the first traces of the coal seam are found in a dark stain in the superficial clay; then a substance like rotten wood is reached, from which all the volatile constituents have escaped. These appear, however, later, and continue to increase as the mine is deepened, until under water or a heavy covering of rock the coal attains its normal physical and chemical characters. Here it is evident that the coal has undergone a long-continued distillation, which must have resulted in the constant production of carbonic acid and carbureted hydrogen. ”

“ The rocks in immediate contact and proximity to coal seams—“the coal measures,” as they are called—are mostly porous, some of them very porous, and thus if at any period of the earth’s long history a seam of coal became heated, as we know so many strata are, and have been heated, a mineral oil would certainly be formed, would first permeate the porous rocks as vapor, then be condensed and make its way through them, following their “dip” or inclination until it reached a barrier such as the limestone forms. ”

“ The irregularities produced by folds, fissures, faults, and partings are not the only ones with which the miner has to deal. So far we have supposed the coal seams to have been laid down in horizontal layers of uniform thickness, with smooth and regular under and upper surfaces. This is true only in a large sense. As a matter of fact each separate seam varies greatly in thickness, and its roof and floor are often broken and irregular. The beds of clay on which the deposits were laid were pushed up unevenly by the exuberant growth of vegetation from them. ”

“ I even venture so far as to affirm that it is not the depth of the coal seams, not the increasing temperature nor pressure as we proceed downwards, nor even thinness of seam, that will practically determine the limits of British coal-getting, but simply the price per ton at the pit’s mouth.
In proof of this, I may appeal to actual practice. Mr. Hull and others have estimated the working limit of thinness at two feet, and agree in regarding thinner seams than this as unworkable. ”

“ In the great coal-field of South Wales, to which we must look for our main supply of anthracite, we are able to trace the action of heat in producing a whole series of different classes of coal in a single seam, which at one part is highly bituminous—soft, flaming coal, like the Wallsend, then it becomes harder and less bituminous, then semi-bituminous “steam coal,” then less and less flaming, until at last we have the hard, shiny form of purely carbonaceous coal, that may be handled without soiling the fingers, and which burns without flame, like coke or charcoal. ”

“ It is important, however, to have the opening at a convenient point near the river or railroad, and it is usually so made if possible, even though the dip should be away from the opening. The inclination is always so slight as not to interfere greatly with the hauling of cars, and it is not much of a task to make a separate opening for drainage. The coal seam is divided by vertical cleavage planes, running at right angles to each other, one of which is known as the butt cleavage and the other as the face cleavage. ”

“ In the anthracite districts, where the seams are sharply pitching, tunnels are driven in the interior of a mine from the workings of a seam already opened across the intervening measures to strike an adjacent seam. In this way two, three, or more coal seams can be worked, and the coal can all be brought out at one surface opening. ”

“ Closed working is adopted when the depth of the overburden is so great that the mining must be conducted underground. The first task in opening up underground coal-seams is to secure access to the seam by means of shafts, slopes, or tunnels. Shafts are vertical openings from the ground surface to the coal-seams. In the United States shafts are usually made square or rectangular in form. This practice is largely due to the fact that timber is used for lining shafts. In Europe round or oval shafts are frequently employed with linings of brick, iron, or masonry.
COAL-MINING ”

“ As it is, we must cross on the surface from the outcrop to the place where the corresponding seam enters the earth. In the southern and eastern anthracite coal districts of Pennsylvania decapitation of folds to a point below the coal [30] measures is general; the coal seams dip into the earth with a very sharp pitch, and the coal basins are often very deep and very narrow, striking into the earth almost like a wedge. In the northern or Wyoming district decapitation is not so general, the angle of inclination of strata is mild, and the basins are wide and comparatively shallow. ”

“ The scars are arranged in a spiral manner the whole of the way up the stem, and the stems often remain perfectly upright in the coal-mines, and reach into the strata which have accumulated above the coal-seam. ”

“ The thickness of coal seams varies in Great Britain from a mere film to 35 or 40 ft.; but in the south of France and in India masses of coal are known up to 200 ft. in thickness. These very thick seams are, however, rarely constant in character for any great distance, being found commonly to degenerate into carbonaceous shales, or to split up into thinner beds by the intercalation of shale bands or partings. One of the most striking examples of this is afforded by the thick or ten-yard seam of South Staffordshire, which is from 30 to 45 ft. ”

“ At various points on these acclivities strata of coal have been discovered partly by the action of water, partly by human labour, the extent of which, owing to the impenetrable forest vegetation and the consequent lack of natural indications, can only be ascertained by boring.
The coal is of the best quality of that kind of brown coal generally called cannel coal, and is occasionally met with in immense seams. The average thickness of the seam is about six feet. ”

“ Nicholas, celebrated for a very thick seam of coal and three or four smaller ones which make their appearance on the side of the range 500 feet above the valley. The large seam is 16 feet in thickness, but the coal, although bituminous, is of a quality that renders it unfit for steam, or gas making purposes. For one or two inches of good bright coal, there are on the average from 12 to 15 inches of inferior earthy matter—in fine bituminized clay. ”

“ It is thus that the Five Quarter coal seam of the mines on the Wear is divided into the Metal and Stone-Coal seams of Sheriff Hill, and that the Low-main seam of the Wear becomes the Five Quarter and Six Quarter seams of the Tyne and Gateshead Fell. Thus also in Brandling and Hebburn collieries a parting of stone first divides and afterwards usurps the place of the High Main coal seam; and thus the two upper coal seams that are well worth working (see the section of Montague colliery north) at Kenton, are no longer so in the neighbouring colliery of Killingworth. ”

“ One of the citizens volunteered to show our friends the coal-mines. While they were making the round of the place he said that a careful estimate showed that the coal-seams now being worked contained enough coal to keep up the present rate of production for five hundred and twelve years. There are thirty-five seams of coal, varying from five to twelve feet in thickness, and one seam—the Greta—is twenty-one feet thick. Nearly five thousand miners are employed underground, and one thousand at the mouths of the mines. ”

“ Besides this main seam, another layer of workable coal, six feet thick, breaks out on the slope of the hills at a greater height. Here almost every proprietor can open a coal pit on his own land, and the stratification being very regular, he may calculate with precision the depth at which coal may be won. ”

“ The seams of stone interspersed through the coal are generally inconsiderable, and amount in only two cases to 27 inches in thickness. The roof of the coal is so unsound, and the height so prodigious, that it could not possibly be worked in one seam, like that of Staffordshire. About 3 feet of the upper coal is therefore left as a roof, under which a band of coal, from 6 to 7 feet thick, is worked on the post and stall plan, with square pillars of extra strength, which are thereafter penetrated. A platform about 3 feet high is left at the sole ”

“ In the early days of coal-mining, open working, or quarrying from Methods of working. the outcrop of the seams, was practised to a considerable extent; but there are now few if any places in England where this can be done. In 1873 there could be seen, in the thick coal seams of Bengal, near Raniganj, a seam about 50 ft. thick laid bare, over an area of several acres, by stripping off a superficial covering varying from 10 to 30 ft., in order to remove the whole of the coal without loss by pillars. ”

“ This is sometimes obviated by holing in the beds below the coal, or in any portion of a seam of inferior quality that may not be worth working. This loss is proportionately greater in thin than in thick seams, the same quantity being cut to waste in either case. The method of cutting coal on the long-wall system is seen in fig. 10, representing the working at the Shipley colliery. The coal is 40 in. thick, with a seam of fire-clay and a roof of black shale; about 6 in. of the upper part, known as the roof coal, not being worth working, is left behind. ”

“ It may very well be doubted whether any single bed of coal is ever more than two or three feet in thickness, and we may therefore take it for granted, that every bed which exceeds that thickness over any considerable space is in reality a compound seam made up of two or more beds resting on each other, with or without "partings" of shale, &c, between them. Not only then are many of the beds which are spoken of under one name in the southern part of the district compound seams, but several of those in the northern district also. ”

“ The first process for finding coal is to bore with iron tools a perpendicular hole in the ground; then if coal is discovered, a shaft, or pit, from ten to fifteen feet in diameter, is sunk, and lined with brick, cast iron, or wood, to prevent the admission of water and the falling in of the sides. When the shaft reaches a seam of coal, passages are made, twelve to fourteen feet wide, and varying in height with the coal; from these proceed smaller ones, which are again crossed by large ones, enormous blocks of coal being left to support the earth above. ”

“ The coal is of exceptionally high quality, as proved both by chemical analysis and by practical experience from its use on a large scale—containing, as it does, only a very small percentage of ash and water, and being free from all impurities. One seam now being worked is specially adapted for steam purposes, rivalling in this respect the celebrated South Wales steam coals, and is being used almost entirely in the large direct Home steamers on their trips from the Colony to Britain, on the refrigerating vessels, and in the colonial steam service. ”

“ All coals less than 2 feet 3 inches thick, are worked with the view of taking out all the coal, either on the Shropshire system, or with pillar-walls and rooms; with this peculiarity, that, on account of the thinness of the seam, the rooms are worked as wide as the roof will bear up; or if a following of the roof-stone, or fall of it, can be brought on, it proves advantageous, by not only giving head-room, but by filling up the waste, and rendering the roads easily kept for the working of the pillars. ”

“ Even seams two feet thick are so hard to work that most of them are left alone, and a seam three feet thick means extra expense in getting out the coal because of the difficulty of labor in hewing and transporting the coal from the face to the shaft. The ideal thickness is between six [Pg 49] and eight feet, where a man can stand upright and can reach to the roof with a slate bar. ”

“ As a rule, every seam of coal rests upon a thicker, or thinner, bed of clay, which is known as "under-clay." These alternations of beds of coal, clay, and rock may be repeated many times, and are known as the "coal-measures;" and in some regions, as in South Wales and in Nova Scotia, the coal-measures attain a thickness of twelve or fourteen thousand feet, and enclose eighty or a hundred seams of coal, each with its under-clay, and separated from those above and below by beds of sandstone and shale. ”