SHAFTS, SLOPES, TUNNELS, ETC.
In the accompanying illustration, figure 139, we present the various modes of mining as pursued in the anthracite coal-fields. The deep, abrupt basin of coal on the left is opened by slope, a, a, in preference to any other mode, as the simplest and most available. The position of the seam, dipping at an angle of 60°, in which the slope is sunk, would indicate it to be the Mammoth. The basin of this seam is reached by the second "lift" in the slope. Each "lift," of one hundred yards' depth, is denoted by a tunnel, c, c, driven to cut the overlying and underlying seams. From the basin of the Mammoth the slope is continued another "lift"—the third—across the measures to the basin of the Buck Mountain bed, or B; and by this means the entire basin is exhausted with much economy, and in less time than it could be made available by shaft.
To the inexperienced this may require a little more explanation. The upper or water-level portion of the seams here denoted is marked out by means of drifts, d, which may be estimated as starting at water-level, and 300 feet from the outcrops, below the engine-house. The first lift of the slope is to tunnel No. 1, 300 feet below the water-level line; the second lift is to tunnel No. 2, or the basin of the seam in which the slope is sunk, which is about 300 feet below the line of tunnel No. 1. The third lift is from the basin of E to the basin of B, and may be 300 feet. This would make the length of the slope from the landing in front of the engine-house 1200 feet long to the basin of B; but the water would only be lifted 900 feet, or to the line of the water level, and by three "lifts." The term "lift" is given to denote the distance which the water is lifted by each set of pumps. It is found by experience that 300 feet perpen dicular is about the maximum height for a column of water to be lifted by pumping machinery; if a mine be 500 feet deep, it is better to divide the column in two lifts than to attempt to lift it in one column. The word lift, therefore, has become a tech
nical phrase to denote, not only the distance which the water is lifted, but also the extent of "breast" found most available in our present mode of mining anthracite coal. It will be noticed that all the coal of the left basin can be obtained by means of this one slope, and the tunnels which are driven to the different seams.
The right basin, however, being wider and more shallow, while the bottom is com paratively horizontal, can be mined by shaft with more economy and availability than by any other means. The distance from the surface to the lower big vein, or B, under such circumstances, would be about 600 feet, and that to the Mammoth, or upper big vein, E, 350 feet. In all shallow basins, where the coal has a low angle of dip, and the basins are consequently wide, shafting is the most available mode of reaching and mining the coal.
In this basin, both drift and tunnel are used to obtain the coal above water-level. The may be such that drifts cannot enter the seams at water-level, and a tunnel is then resorted to; but the distance from the tunnel c, c, to the outcrops of the seams is too great to be mined economically by one set of breasts or chambers, particularly when the angle of dip is as low as here represented,-30°: therefore a "counter-level," or drift, d, is driven into the seam between the tunnel and the outcrop, and the coal brought down to the level of the tunnel by inclines. The position of the coal-breakers and out side improvements is denoted by the buildings in connection with the respective basins. This illustration, if properly understood, will convey a better impression of the modes of mining generally in use than could be given by pages of description: we therefore briefly call attention to the letters in the engraving, and leave the reader to find out" what we may have omitted. A glance will be sufficient for the practical to comprehend the whole.