This is a mode generally made use of in flat seams, or where the dip is about 5°. The chambers are turned off from the main avenue or gangway at right angles, and the railroads for the mine-cars take up one or both sides of the breast or chambers, while the air is carried up one side and down the other. This plan is frequently modi fied by cutting "headings" from one breast to the other, as shown in No. 7, and carry ing the air along the face of each, as shown in No. 2. The arrows indicate the course of the air. This plan will come under consideration again in No. 7.
This is an offset that becomes necessary from the change of pitch, which increases from 5° to 10°, as shown by the figures. This mode might be continued through No. 3 with benefit, we think; but, as it is not consistent with the plans generally adopted, we have given those which are. It will be noticed by those who are familiar with such matters, that the change from No. 1 to No. 3 becomes necessary in consequence of the change of dip: while No. 1 runs off at right angles to the gangway, No. 3 runs off obliquely in order to accommodate the grades of the railroads to the dips of the seam. This oblique course leaves an angle or corner which No. 2 removes; and, as it is not desirable to start off chambers of this character near the shaft, a larger corner is allotted to No. 2 than is absolutely necessary. The air from No. 1 circulates through No. 2.
The general mode of mining coal from pitching seams which are not steep enough to "run" the coal down the shutes, and yet too steep to take the cars in any direction the miner may choose, is given in this plan. The course of the chambers or breasts, and, consequently, of the tram-roads following them, is at greater or less angles with the gangway, according to the dip of the seam. If the dip is 10°, the course may be nearly at right angles, but if 30°, the course must oblique slowly from the gangway and run nearly parallel with it. This mode, therefore, has serious objections, since no order or system can be continued unless the dip of the seam is uniform, and then no perfect system of ventilation can be preserved in extensive mining. The objections are so numerous that we do not think it profitable to argue them. The mode of ventilation commonly adopted is by "cross-heading" at intervals from one breast to another, or by carrying the air up one and down the other,—both being alike objectionable and dan gerous in a fiery mine, from the fact that the gas is carried a great distance with its gathering impurities, past the face where the miners are at work, and, consequently, can furnish only impure air to the outside breasts, and may become inflammable enough to ignite from the miners' lamps.
This mode differs essentially from those mentioned in the foregoing plans. They (Nos. 1, 2, and 3) require the car to enter the chambers and follow the miner, taking the coal from his hand direct to the surface; but Nos. 1, 2, and 3 can be used to advan tage only when the pitch or dip of the seam is below 25°; when it is over that, "shutes" instead of railroads are made use of, as shown in plans 4 and 5. In plan 4 the shute is carried up the centre of the breast. In small seams it is a passage or way about 6 feet wide up the middle of the breast, secured by timber on each side, and against which the refuse of the mine is packed on the outside. An avenue or incline is thus formed directly up the pitch of the seam and at right angles with the main gangway. Into this the coal is thrown by the miners or their assistants, and down the smooth incline formed by the bottom slate of the seam the coal slides to the vicinity of the gangway, where it is loaded into the cars. This plan is perhaps improved by that of No. 5, in which the shutes are carried up on each side of the breast and against the sides of the pillars, in which case there are two shutes to each breast, but only the same quantity of timber required, as a single row of "props," parallel with each pillar, is sufficient. In either case the air is generally carried up one breast and down the other, or along the face of the breasts, going up the inside one and down the outside one; but most of the anthracite collieries worked on this plan are small red-ash seams above water-level, and the air in such cases generally escapes through an "air-bole" ascending to the surface from one of the breasts. In large collieries below water-level, improvements are required which will be illustrated farther on. Many of our collieries, however, are still worked on this principle, and they are, consequently, often troubled with "bad air," and interrupted by falling rock or "crushes" in the abandoned portions of the mine, through which the air is necessarily carried.