taken direct to the working places, self-acting inclines or winches being employed.

Other moderately inclined seams are worked by the system called "tailles chassantes" (Fig. 233). A road is carried up from one level to the other, and branch roads put off right and left, about every 15 to 20 yards, measured along the inclination of the seam, taking out the coal for a distance of from 50 to 100 yards on each side of the main incline, the face, as before, presenting a series of steps, but its direction in this case is parallel with the inclination of the seam; at intervals diagonal roads are put up through the gob, cutting off the level roads as illustrated.

The relative advantages of the two latter systems have been exhaustively compared by Mr. Cambessédès, whose conclusions may be briefly summarised as follows:-When working towards the rise (tailles montantes) weight is favourable to the bringing down of the coal, and produces a sensible reduction in the cost, amounting in certain cases to as much as 25 per cent., while in all cases where such working places are served by shoots through the gob there is a greatly diminished cost in the driving and propping of such roadways com

At an

pared with the system of forward stalls (tailles chassantes), which are served by ordinary tubs of average carrying capacity. inclination of from 5 to 8° up to from 20° to 22° it seems preferable to employ the latter system, and to construct a self-acting incline through the gob, which can serve several levels; indeed, if the tubs are to be taken into or near the working face, steep inclinations above 30° to 35° are unfavourable to working towards the rise, because the tub is apt to throw out part of its contents, and because the cost of repairs to the rolling stock is large on account of the violent usage it receives. In a seam giving off large quantities of fire-damp, the method of forward stalls (tailles chassantes) is advantageous, because the gas tends to accumulate in the superior angle of the stall, and the workmen who are distributed along the face are away from the fiery zone, as the gas can pass away to the upper level, while in working towards the rise (tailles montantes) fire-damp has a tendency to extend along the working face, where the hewers are employed. Should the face be other than perfectly straight, a dead end may be formed, which the air current clears with difficulty. In the system of tailles montantes the stalls are divided into two parts, and the operations of the workmen are carried on more independently of each *Soc. Ind. Min. (3e Serie), ix., 551.

other than those of the men employed in tailles chassantes. As a result, in workings of the former system a greater number of men can be employed with less inconvenience to each other, thereby realising for that method all the advantages of rapid working as:-reduced cost of timber and maintenance; a larger proportion of round coal, and sometimes reduced cost of getting; the haulage staff better employed; and fewer slips and falls. These advantages are, however, minimised, by the fact that when the tubs are taken to the face, more plant is required with tailles montantes than with tailles chassantes, and there is a greater amount of wear and tear. In the former case, the length of the inclined plane is continually altering, and the brake wheel has been moved at a cost, in some instances, of about 9d. per yard. Not only so, but it is difficult to regulate with exactitude the length of the ropes each time the pulley is raised, and as a result, collisions are frequent and the rolling stock deteriorates rapidly.

The extra cost of working seams lying at angles of from 30° to 50° is considerably larger than that of moderately inclined ones, probably as much as one-half more, in some instances frequently a third, but over an angle of 50°, unless the seam is thick, tender, or liable to spontaneous combustion, it can generally be mined cheaper than if it was inclined between the above-named limits. There are some compensating advantages connected with the working of steep seams which are absent in flat ones, the most important one being the ease with which faults are recovered. In beds of moderate inclination a fault throws the measures up or down, and a recovery of the seam is only possible by an alteration in the level of the roadways, which entails considerable expense. In steep seams the throw of a fault is sideways, and all that has to be done when one is met with, is to turn the level to the right or left hand, a less troublesome and less expensive matter than lowering or raising it.

Working Thick Seams-South Staffordshire. No matter what system of working is adopted, the invariable rule in the Ten-Yard seam is to drive out to the boundary and bring back the work, leaving the gob behind. Two main gate-roads proceed along the strike of the seam, serving as haulage roads, and the distance between them varies from 33 to 45 yards, being always such that in the operation of getting coal these preliminary drivages will form a portion of the chambers, and, as it is called, come in to work." Where a large area is to be won, roads are branched out right and left of the main roads, and coal gotten at the extremity of these, even before the former have proceeded much past them, the only precaution to be adopted being, that the coal so worked should be a sufficient distance from the shaft not to affect it by any subsidence. While this portion is being worked out, the main roads proceed on their course, and branch roads are again sent out at suitable distances, and when they reach the boundary, either of the lease or of the district, work is opened as before.

at once.

The methods of working commonly employed may be divided into (a) square work, and (b) longwall, the whole thickness being removed True longwall is, however, unknown in the thick seam. It might preferably be defined as bord and pillar, the large blocks being pillars. If so, the system of working is the same as the one pursued under the same title in the Northern coalfield; the removal of the pillars being similar with modifications occasioned by the

greater thickness.

The coal is sometimes worked in two divisions

by a modified longwall system, but although this possesses some advantages, yet the numerous practical drawbacks, such as the increased quantity of small coal produced, the inferior mineral obtained when working the lower slice, and the frequency of gob fires, have resulted in its general abandonment, except in a few isolated special cases.

(a) Square Work. In this system the coal is worked out in a series of rectangular chambers, separated from each other by ribs of coal, internal support for the roof being afforded by a series of square pillars of solid coal. The old method of opening a side of work was to drive a series of stalls 10 yards wide, leaving 10 yards of coal between each, and then a second set of 10 yard stalls at right angles to the first, the result being that pillars 10 yards square were formed. This operation would be carried out in the bottom coal, the top coal being got by the method described a little further on. Practically, however, opening a side of work in this way is a thing of the past. To do it with any success requires an exceedingly strong roof, and even then coal is not got out so clear as it should be. At the same time, it is advisable to drive the stalls, in the first instance, at least 5 yards wide, and so save the cost of narrow work.

With an average roof a convenient size for the openings is 10 yards wide, and for the pillars 8 yards square, and in such case the ordinary gate-roads opening out a district will be driven, leaving a piece of coal 33 yards wide between them. On reaching the boundary of the district the two gate-roads will be connected by a crossdrivage (a, Fig. 234). This will be widened out by "side-laning," which consists in treating the side of the road as a longwall face, and holing it out to a depth of 10 yards, as shown at b. While this is being done a second cross-drivage, c, about 5 yards wide, will be carried between the two gate-roads, cutting off a block of coal 8 yards wide. The side gate-roads will then be side-laned off to 10 yards wide, d d, and a stall, e, driven through the block of coal remaining, the position now being that two pillars 8 yards square are surrounded on three sides by openings 10 yards wide, and on the fourth side by an opening 5 yards wide. All this has been carried in the lower 6 or 7 feet of coal.

In the back opening the top coal will now be got down in sections, slice after slice being removed vertically. The whole distance across this opening is not attacked at once, only a certain portion of its length being worked at a time. The top coal is got down by cutting vertical grooves up through the overlying measure of coal, leaving between each length of 6 feet what are called "spurns." These spurns are narrow webs of coal holed through in the upper part. When the layer that is being attacked has been cut through in this manner on both sides, the spurns are reduced by the aid of a pick, and are then finally "jobbed" (knocked) out with a "pricker," which is a long instrument very similar to a boat-hook. Α spurn is always left at the face, and when this is removed the whole mass falls, and is then in a position to be taken away by the loaders.

While this is going on, a third cross-cut will be driven between the two main gate-roads at a distance of 13 yards from the last one (a, Fig. 235). The opening (c, Fig. 234) is then widened out to 10 yards, as shown at b (Fig. 235), the main road side-laned off as before, cc, and

a middle thurling, d, 10 yards wide, driven across, forming two more pillars 8 yards square. While this is being done in the bottom coal, the top coal has been got down around the two pillars shown in Fig. 234. A fourth cross-drivage is made between the two gate-roads at a distance of 13 yards from the last one, and the pillars there cut off, as already explained, so that at this stage of the operation the side of work considered will have the appearance shown in Fig. 236—viz., six pillars, each 8 yards square, surrounded by a series of openings, 10 yards wide. The top coal by this time will be removed all over the side of work, except on the three sides of the last two pillars, and will

Fig. 234.

Fig. 235.

Fig. 236. gradually be got down there until nothing remains. Fire-dams will then be put in at the points a a, and a new side of work started, cutting off a rib of coal 8 yards wide.

(b) Longwall in One Division.-Gate-roads are first driven out 7 feet wide, leaving 40 yards of coal between. The cross-holings are 45

C

α

X

Figs. 237, 238, and 239.

yards in the clear, so that the commencement of each district is to subdivide it into pillars, 40 yards by 45 yards, such dimensions allowing of all the roads coming into work. Upon reaching the boundary of the district, the removal of the coal is commenced by widening the 7 feet gate-road (a, Fig. 237) to 8 yards, this being carried. on all across the face. While such is being done, a narrow stall, b, 4 yards wide, is driven parallel with it, cutting off a rib of coal 21 feet in the clear, and then this rib is split into pillars, 7 yards square, by a series of cross-drivages, ccc, each 4 yards wide. The block of coal between two roads is thereby divided into four pillars and three openings. This work is carried out in the lower 6 feet of coal, and while it is being done the top coal in the 8 yards back opening is got down by cutting through and dropping down the successive layers.

The removal of the pillars is carried out as illustrated in Fig. 238. Cogs of timber and stone, a a, are built in the stall next to the gateroad, and the central stall widened from 4 to 8 yards, a slice being taken off the pillars on each side. The top coal is got down in the

opening so formed in the usual manner. The cogs are then removed, and placed in the position shown by the X. The remainder of the pillars are then got out, together with a portion of the two pillars on the side of the original gate-roads. Fig. 239 now shows the position of affairs. The two pillars remaining in this block, together with the two half pillars of the adjoining blocks, are removed in a similar manner, cogs being built at c for this purpose.

During the whole of the above operations, half the coal produced goes down one gate-road, and half down the other, as shown by the arrows, the tubs being taken straight into the face. While this has been going on, another row of 7-yard pillars and 4-yard openings have been cut off in the bottom coal, and the pillars removed in a similar manner. This operation is repeated, until such time as fire breaks out. A rib is then cut off, dams put in, and workings again opened on the other side of it.

For the success of this system it is necessary that the coal should have a soft roof, and one that comes down quietly without much weight. In some parts of the coalfield there is a very hard roof which will bear a large amount of weight without collapsing; however, in the words of the collier, "when the weight does come on" nothing can stop it. Such a roof is very unsuitable for this system.

The advantages claimed are: the greater first yield and total clearance of coal.

The disadvantages are: the large amount of slack produced (this being due to the quantity of gunpowder employed), and the smaller total yield per acre. A greater quantity is obtained per acre than by the first clearance in the square-work system, but, after the lapse of considerable time, the ribs and pillars left in this latter method of working are cleared out. In many cases, the remnants of the thick coal are worked a third time, thus obtaining a further yield. The total produce of winning the broken is about one-third of the quantity obtained by the first working, of which one-third will be coal, and two-thirds slack. The expense of winning the broken mine is somewhat greater than that of getting the solid coal.

In every system of thick coal-mining, dip work is advantageous, as the falling roof-stone rolls away from the workmen.

Pennsylvania. The system of working the Mammoth Bed, which sometimes attains a thickness of 60 feet, as described by Messrs. H. M. Chance and Franklin Platt,† is similar to the double stall method of South Wales. Either from the bottom of the shaft or out of a slope, if no shaft is sunk, a main road, called a "gangway," is branched out right and left, but for the sake of not weakening the roof, the two openings are not placed quite opposite each other but nearly so. Gangways are not driven truly along the strike of the seam, but are graded slightly (about 6 inches in 100 feet), in order that the full waggons may be moved easily, and water drain to the slope where the pumps will be situated. A parallel road some few (10) yards away, called a heading, is driven for the purpose of ventilation.

As soon as the gangways have proceeded so far that the subsidence

*Second Geo. Survey of Pennsylvania. Report A. C. Coal-Mining.

+ Ibid. Report A 2. Coal Waste. The chapter on Mining is by Mr. J. P. Wetherill, and is an expansion of a paper originally contributed to Amer. Inst. M. E., v., 402.