enter the main workings from the surface or from the quicksands in the overburden.

The Pittston bed supplies two examples of the same method of supporting the roof under built-up parts of Pittston. (See figs. 56 and 57.) In this particular district a great number of fissures in

the overlying rock extend from the top of the coal bed to the overburden; in consequence the roof is exceedingly weak and requires extra support. These fissures may be only a few inches across or as much as 5 to 6 feet.

Replacement of coal with rock put in by hand is obviously expensive. In fact, it can probably be done only at a great loss; but the

coal is conserved and might not have been recovered if this method of mining had not been used.

Cost of work.—To give some idea of the tremendous expense that such work entails in this district, it may be stated that the 34 men employed produce daily only 20 cars of coal (40 tons), or a little more than 1 ton per man. Ten of the men unload and pack rock in the rooms that have been completed; 8 miners and 8 laborers are also employed. These 1G men actually produce the coal at a rate of a little more than one car of coal apiece. As the amount paid per car does not enable them to earn a living wage, these men are placed on the consideration basis, and the miners receive $8.80 a day and the laborers $6.60 a day. The additional 18 workers are company men employed at something more than $5 a day each.

Although these costs are high, the company is enabled to increase its output from this colliery by mining this coal without increasing the overhead. The mining of the coal also tends to reduce the taxable value of the colliery and therefore the amount paid in taxes, but these two factors are inconsiderable.

There are other places in the anthracite region where other companies could do work of this character and thus conserve the steadily decreasing supply of anthracite.

SUMMARY OF MINING METHODS

In preceding chapters of this bulletin the author has discussed the various types of mining methods that are in use or have been in use in the anthracite region. The progress in the art of thin-bed mining has been shown, and some of the opportunities for improvement have been indicated. The author now proposes to show to what degree these different types of mining are being used in the anthracite region.

MINING ADJACENT BESS

In the section on " Mining of adjacent beds," which covered the mining of beds separated by a thin parting, the author pointed out that mining conditions naturally vary as the character of the beds varies. The roof, the floor, the thickness of the partings, the pitch, and the type of coal determine to a great extent the method of mining that must be developed. Generally speaking, however, two virgin beds can best be mined simultaneously.

When first mining has been completed in one bed, whether it is the over or the underlying one, the best results seem to be attained when the pillars can be columnized. Unfortunately, columnization is not always possible because of the inaccuracy of the early surveys and the manner in which many pillars were gouged, as has been already

One point needs stressing; that is, that in virtually every mine the author visited where two adjacent beds were being mined the company was driving gangways in both beds, even though the parting between the beds was comparatively thin, a procedure that at many places seemed unnecessary. In the cleaning up of the old gangways in the bed below—this cleaning up has to be done in time—all of the coal in the overlying bed can be recovered, or if the coal beds are virgin those systems of mining which obviate the need of two sets of gangways can be employed.

LONGWALL AND SEMILONGWALL MINING

Comparatively little longwall or semilongwall mining has been used in the anthracite region. Most of it has been done in the Northern field, particularly by one company. Another company has used the method three times with great success, but all its other attempts to install longwall mining have proved unsatisfactory. However, talks with various officials of this company indicate that the unsatisfactory results were due to the men in immediate charge and to the attitude toward labor rather than to the use of the longwall system.

Furthermore, many companies had not tested this system because they do not experiment but are willing to wait for some one else to work out the system for them. Unfortunately most companies in the anthracite region are unwilling to spend in experiments on mining methods the time and funds they will give to other work around the mine. The reason that they are not willing to experiment is not evident. Probably they fear that coal may be lost or labor antagonized, or they do not care to invest the money in such work. However, if more money were spent in well-considered experiments, the greater recovery that would probably result and the cheaper methods of mining that would probably be developed would more than justify the cost.

Only 36 longwall or semilongwall faces were being mined in 1925 in the anthracite field, so one can readily see that longwall or semilongwall mining is not in wide use.

SCRAPER MINING

Scraper mining probably has an established place in the anthracite mines, for there are certain conditions under which it gives excellent results; however, the method has some serious defects. Scrapers can be operated in low beds of coal, and the writer has seen them working in places where the bed was not more than 18 inches thick. Their use enables a considerable saving to be made, because rock does not have to be brushed from the roof of rooms, as is necessary when mine all of the supplies that the miner needs, and thus save him considerable hard work.

The use of scrapers, however, has limitations. Scrapers should not be used where the floor is rough, as they cause the coal to bounce and break and thus entail considerable loss in prepared sizes. They should not be used where the bottom is soft, for they have a tendency to lift the loose floor material as they are dragged along, mixing it with the coal and increasing the amount of refuse that has to be removed in the breaker.

Scrapers have one advantage. Whether the grade favors or is against the loaded scraper makes little difference; the scraper can be operated up grade as well as down. If, however, the grade changes abruptly, trouble ensues, and it may be necessary to bridge across such places. This condition was mentioned twice in the section on " Scrapers." At the time of writing (1926) 164 scrapers were in use in the anthracite region.

SHAKING CHUTES

The most flexible type of underground mechanical conveyor in use in the anthracite region is probably the shaking chute, which can be used as readily in low coal as in high. Its capacity is almost unlimited, for it can handle as much as 50 tons of coal in an hour. Its capacity depends directly on the grade and the number of strokes per minute, but can be further increased when the grade is level by giving the chute a jerking motion through the drive itself or by bumps applied directly to the shaker.

Such a chute can be used successfully in beds as low as 18 inches and in beds of any height above the lowest. It can operate on any grade from level to that on which coal slides on sheet iron. In a few instances it has transported the coal up a grade for a very short distance, but at a great reduction in capacity.

The shaking chute is economical in the use of power, particularly when an endless rope drive is used. At one colliery as many as eight shakers operating on an 8° pitch have been driven by one 15-horsepower engine. Two additional shakers were attached to four of them, so that the downward stroke by gravity raised the other two shakers, which were therefore operated without using additional power. The cost of repair and upkeep of shaking chutes is low when the chutes are properly designed and maintained. The chutes can be bent to go around any curve, and hence can be used successfully in second mining. They can be used on a longwall face.

Degradation is reduced to a minimum by their use, and it is not necessary to keep a man on the gangway to look after the loading of loaded into the shaker chute, and when he thinks the car is full he can go to the gangway and top it off. The drive often can be so arranged that the sections of the shaking chute and the supplies that are necessary for producing the coal can be transported to the face.

Unfortunately, in the design of shaking chutes American operators did not begin where the English and Germans stopped but went back to the point where they started; as a result, the design of these shaking chutes is not what it should be, and is much inferior to that of shaking chutes now used in Europe. Some excellent lessons can be learned by a study of these European shaking chutes and can be applied successfully in this country.

In the anthracite region 103 shaking chutes were being used in 1926.

SILTING

One mining practice that has been developed to highest efficiency in Germany is the silting, slushing, or back-filling method used in all parts of the anthracite region, but probably most extensively in the Northern field. This method originated in the anthracite region of the United States and has been used and adopted extensively in other countries.

Silting was originated by a Catholic priest in the city of Shenandoah. In the late sixties he was rector of a church under which the Philadelphia & Reading Coal & Iron Co. was mining. Subsidence began, the walls of his church cracked, and the whole building was in danger of destruction. He complained to the coal company and was advised that everything known to engineering practice was being done to give the necessary support to the building, but still the subsidence continued. As a result of the continued damage to the building he went to the president of the coal company in Philadelphia, related his troubles, and was advised that the company was willing to do everything in its power to save the church, but did not know what else to do. Before going to interview the president the priest had worked out and outlined on paper a plan for depositing breaker refuse in the workings. The company told him that it was willing to test the method he suggested, but was afraid that it would not be successful. Contrary to their expectations it did stop the movement of the ground. The silting methods now in use originated thus and are about the same to-day as in the decade from 1860 to 1870. The chief improvements have been in the mechanical methods of preparing the silt and transporting it to the underground workings.

So far only a small amount of second mining has been done in silted areas, so the results that may be anticipated are not fully de