Allegany Coal-fields. — The great Allegany coal measures consist of a deep series of strata, which include gray sandstones, shales, bituminous shales, slate-clay and fire-clay, carbonate of iron, and coal, aggregating in thickness about one thousand five hundred feet. The whole series has been curved downwards a few degrees, and hence the ends are uplifted on both sides of the basin, in Davis and the Great Savage Mountain. Its entire length from northeast to southwest is estimated to be about thirty miles, but this includes that part of the basin which crosses into West Virginia, as well as a portion in Pennsylvania. The surface has suffered such deep and wide-spread erosion since the deposit of the upper strata of coal that perhaps less than one-half of this important fuel now remains where formerly it constituted one continuous sheet over the whole expanse of the valley. It may be noticed that the two ridges of mountains bounding the basin run nearly parallel, and thus give the longest possible exposure of the strata along their flanks. Fortunately for mining, the forces which have operated to carry away such vast areas of the surface have also cut longitudinal deep troughs, through which the rivers and creeks now run, into the subjacent strata, and have thus laid bare the edges of all the seams of coal. Near the upper end of the basin a transverse ridge, nearly equaling the adjacent mountains in height, connects Davis Mountain with the Great Savage, and cutting off about one-fourth of the valley, turns the streams to the east, to be precipitated through the gap into Will's Creek. On the western part of this ridge also stands the town of Frostburg, from which this upper basin takes its name. The lower division of the great coal basin extends down with a gentle slope towards the Potomac River, and is traversed in nearly its whole length by George's Creek, which runs through a trough scooped out of the coal and hard rocks to a depth of more than twelve hundred feet. The Potomac River has likewise cut a deep and wide trough across the southern part of these measures, leaving the strata exposed in a section more than one thousand feet thick. Besides these, numerous creeks and brooks have cut across it from the mountain flanks on both sides, thus intersecting the coal-seams and dividing them into small areas. In the northern valley, Braddock's Run and Jennings' Run, with their tributaries, also cut deep into the coal-rocks and expose their ends. The former rises near Frostburg, receives the waters of Preston's Run, and after flowing eastwardly for about six miles, passes through a gap in Davis Mountain and empties into Will's Creek two miles northwest of Cumberland. Through this natural avenue the Cumberland and Pennsylvania Railroad finds a way up the heavy grades to Frostburg, and from thence transports the coal mined in this region; but the coal mined in the larger basin, farther south, finds a natural outlet in the direction of the Potomac River, and is accordingly carried by rail to Piedmont, to be transferred to the charge of the Baltimore and Ohio Railroad.
The great importance of these coal measures to the State and country at large seems to justify the detail which is necessary to a correct understanding of the resources of this region. Through the careful surveys made several years ago by the State geologist of Maryland, Philip T. Tyson, a section was drawn showing the whole series of strata included in these coal measures, and giving measurements of all the beds of coal in their order of succession from above downwards.
No less than thirty-six beds of coal have been originally laid down in this region. Some of these, however, range at present from only a few inches to a scarcely workable thickness of not more than two to two and a half feet. But, besides these more numerous beds, there is a grand aggregate in ten others which amounts to a total thickness of fifty-four feet of good coal. At the present time the great " Fourteen-foot Bed," as it was then called, is so accessible and easily mined that attention is almost entirely diverted away from the narrower and consequently more difficult ones. The system of mining is, however, still so wasteful that the narrower beds will no doubt be brought into use before the end of the present century. Greatly to the advantage of mining in this region is the order in which the strata have been laid down. They rest one above the other in regular layers, no faults or serious dislocations having been found in any part of their extent, and accordingly they can be excavated continuously without the hindrances occasioned by having to search for the broken ends thrown out of level. With regard to the mining of this great deposit, Prof James T. Hodge reports, —
"At those mines now worked in the northern end of the basin, the real thickness of the bed is about eight and half feet, and still farther to the northeast the bed becomes thinner and poorer by increased intermixture of seams of slate. In the central portion of the basin, although its thickness may reach twelve feet, there is hardly a mine in which it can be said that more than ten feet of coal is worked to any extent, while the most of them save only about seven feet. Various reasons are given in explanation of this. In some mines the slate roof over the coalbed when undermined is apt to fall in blocks or ' slips,' and endanger the lives of the miners. In these mines it is almost a necessity to leave the upper two or three feet of the coal-bed for a safe roof, and remove only the middle and lower portions. The roof coal, as it is called, is often more or less streaked with layers of 'bony coal,' a variety duller and more compact than the rest, but otherwise entirely unobjectionable. Merely on account of this appearance this portion of the bed is entirely lost, even when the overlying slates would make it as safe a roof as the coal itself. In some mines, at the Borden Shaft, on George's Creek, where the roof coal is left to the thickness of about two feet, and from nine to nine and a half feet taken out below it, a portion of the upper coal is expected to be saved, when the pillars are finally removed and the whole roof is allowed to come down.
" But the roof coal is not the only part left unworked at many of the mines. Throughout the whole coal-field the lowest two or three feet of the bed contain one or two seams of slate, each half an inch or so thick and about a foot apart. In the destructive rivalry that has existed in the different companies many have allowed their ' bench-coal' to remain unworked, and have been willing to pick out the choicest middle part only and sacrifice all the rest."
This will suffice to show how imperfect the system of mining has been, even in quite recent times, but extended experiences suggest more exact methods, and the work of the future will be conducted with increased precision, as the laws governing the pressure, elasticity, etc., of the associated layers of rock and coal are more closely watched and studied. These coal-beds have been built, as others of similar character, by the slow accumulation during long periods of time of dense forests and thickets of trees and plants related to our present club-mosses and horse-tails. These plants in the age now current are of small size, scarcely any of them exceeding a foot in height, while most are but four or five inches; but, during the carboniferous epoch, they covered the marshes with examples as large as the great pines and swamp-cedars, and which, falling, left their huge bodies in deep deposits in the mud and water. These became covered by clay, sand, and decomposed rocks, as each stage of development was reached, and by the great pressure of the weight accumulated above, accompanied by slow, mild heat, were finally converted into the coal-layers now so useful as fuel. In the shale accompanying the more important part of the coal, vast numbers of impressions of the twigs, leaves, buds, etc., of the trees, plants, and ferns of the epoch remain imbedded, testifying to the form, proportions, and character of the flora which once tenanted the beds.
The main coal-field of Allegany County is embraced between Davis Mountain on the east, the slopes of Savage Mountain on the west, the Potomac River on the south, and Mason and Dixon's line on the north.
The whole extent of this area, called the eastern coal-field of Allegany, is about thirty miles in length by an average of four miles in breadth, making altogether one hundred and twenty square miles lying in Maryland. The figure of this coal-basin is slightly curved from north to south, and rises sometimes from its longitudinal axis to its eastern and western borders, resembling in shape an Indian's canoe, except that its sides are not so perpendicular. On the