This mode has several modifications, and may be considered the best in use in the anthracite mines. The illustration conveys but an imperfect impression of this style, and only gives one illustration of it. It may be noticed that the air passes up one Shute and down the other in the same breast. This is not the best or the general plan. It is more frequently carried up one breast and down the other by "cross-heading" the intervening pillars. But perhaps it is as usually carried up the inside breast and along the "faces" of the breasts through occasional cross-headings, and down the outside breast. The second plan is better than the first; but between the second and the third there is not much difference. When the chutes are long, foul air is apt to gather in them, unless a current is kept in circulation through them ; and in this respect the second mode is preferable to the third; but both are defective, from the fact that the entire impurities of the mine are swept along with the current through all the breasts, and the gathering gases and foul air must accumulate and become obnoxious in the outside breasts. This is the great evil in all our modes of ventilation. The air is carried in an unbroken current through the entire mine, sometimes traversing many miles of air-courses, and carrying the foul air and gases from one breast to the other, from the inside miner to the next outside, to the end. It not only makes the current weak, but it can furnish only impure air to a large portion of the mine.
We have given a part of the excavated portion of the mine, or goaf (gob), in plan 5, representing portions of the pillars "lost ;" but this is a favorable exposition. We have no doubt that from one-third to one-half the coal in our large beds is " lost" by this plan of mining ; and we cannot see how it can be otherwise, since the immense pillars, except their upper portion, must stand until the entire mine is worked to the boundary before they can be "robbed," or "worked back ;" and when this comes to be done, the immense weight of the superincumbent strata brings on a " crush," which ruins most of the coal and prevents the remainder from being obtained, so that none or but little of the nume rous and massive pillars, left by our present system of mining can be obtained. In both respects,—in ventilation, as well as the economy of coal,—the mode of mining generally in use in the anthracite regions is not only seriously defective, but wasteful, dangerous, and ruinous.
There are exceptions to this sweeping charge; but they are few and far between, and we have rarely met with a well-ventilated and economically mined colliery in this country.—much to our surprise ; since the best of English talent is employed in the anthracite regions, and we cannot accept the maxim that the English modes do not apply to our formations. We hope to prove conclusively that we are not only following
the most wasteful, imperfect, and costly methods, but that the improved and long-tried English plans of ventilation and mining can be successfully modified and applied with much economy to our anthracite mines ; while for the bituminous regions they are just the plans required.
This is a modification of No. 2, to conform to the greater angle of dip, which increases from 5° to 30°. It is the same in principle as No. 3, and is much in use where the angles of dip are within the degrees specified. This and the preceding modes—plans Nos. 4 and 5—are in general use in the anthracite regions, but are both open to the same objections in regard to ventilation and the waste of coal ; and no order or system can be successfully pursued that is not liable to sudden derangement from the frequent changes of dip. The ventilation in plan No. 6 is susceptible of a change from the mode given, which is perhaps the best in works of small extent ; but when more extensive the air is taken down one chamber and up the other.
The cars are taken into the breasts or chambers in all such cases: they follow the miner and receive the coal from his hand, taking it direct to the surface. Where the dip is considerable, the railroad (tram-way) is carried on the lower side of the breast or chamber, against, and parallel with, the pillar. If carried through the middle of the chamber, when the dip is considerable it would occasion much labor in handling the coal up from the "dip side," and would also prevent the drainage of the water from the lower side of the chamber ; but when the road is carried on the " dip side" it forms an escape for the water, and enables the miner to slide his coal down the incline of the seam from the upper portions of the chamber to the vicinity of the car, and thus saves handling. These breasts or chambers are carried from 16 to 30 feet wide, according to the nature of the top and the size and character of the seam.
This is a simple modification of No. 1: they are both worked on the same principle. In this case the roads are carried through the middle of the chambers instead of the sides, and the air passed up one breast and down the other ; though it is perhaps as frequently carried along the faces, by going up the inside breast and down the outside one.
These chambers, like those of No. 1, are taken off at right angles from the gangway or main avenue, and can be successfully used only when the dip is about 5° or less, —which is not of frequent occurrence in the anthracite regions, except in the Scranton district of the Northern coal-field.