OUTPUT. The world's annual production at the present time is about 850,000,000 short tons; the output in 1900, according to The Min eral Industry, was distributed as follows: It is interesting to follow the progress of the United States as a coal-producer. In 1S6S Great Britain produced 3.6 times as much coal as the United States, while Germany's product that year was 15 per cent. greater than that of the United States. In 1871 the United States exceeded Germany's output by about 10 per cent., but afterwards fell back to third place until in 1877 she once more sprang forward, and gained on both Germany and Great Britain. In 1899 the United States led the world, and sup plied nearly 32 per cent. of its production.
The average price of bituminous coal at the mines in the United States, per short ton, varied between 1893 had 1900 from $0.80 to $1.04; while that of anthracite was between $1.41 and $1.59 for the same period. The total number of laborers employed during 1900 was 449,181, of which number 144,206 were anthracite miners.
During the closing years of the nineteenth cen tury European countries have been confronted with a most serious problem—the exhaustion of their coal-supply. This condition was empha sized in 1899 and 1900 by the occurrence of strikes in the Wales coal regions, by war in South Africa, and by a stimulation of industries in Germany which required much additional coal. Prospecting having shown hut little re serve material. the most natural result was to look to the United States, and in 1900 there began a movement of coal to Europe, which may before many years assume large proportions. Ocean freights are the present great drawback.
IIINrsc OF COAL. The presence of coal in pay ing quantities having been determined by pros pecting and geological surveys, the next consid eration is to extract this coal from seams. No definite rules can be given for the selection of a method of mining that will cover all conditions; each mine furnishes a distinct and separate problem. Every system of mining, however, aims to extract the maximum amount of the de posit in the best marketable shape and at a minimum cost and danger. Speaking broadly, all methods of mining come under the head of either open working or closed working. Open working is employed when the deposits have no overburden of barren rock or earth, or where this overburden is of such small depth that it can be easily and cheaply removed, leaving the coal deposit exposed. The mining of such ex posed seams of coal is really a process of exca vation or quarrying, and the machines used in making open-pit excavations and in quarrying are applicable to the work. Closed working is adopted when the depth of the overburden is so great that the mining must be conducted under ground. The first task in opening up under ground coal-seams is to secure access to the seam by means of shafts, slopes, or tunnels. Shafts are vertical openings from the ground surface to the coal-seams. In the United States shafts are usually made square or rectangular in form.
This practice is largely due to the fact that timber is used for lining shafts. In Europe round or oval shafts are frequently employed with lin ings of brick, iron, or masonry.
Generally the shafts are divided into two or more compartments, in each of which is installed an elevator for hoisting the coal-ears to the sur face. The number of compartments in a shaft and their arrangements depend upon the par ticular use to which the shaft is to be put, the number of shafts employed, and their depths. Where the seams are comparatively near the surface, it is usually cheaper to sink a number of two or three compartment shafts than it is to haul all the ore to one large shaft; while, when the shafts are very deep. it is preferable to sink a smaller number of four or six compartment shafts and extend the underground haulage to a single shaft over a great area of the workings. Where timber lining is employed, a stronger construction is obtained by placing the com partments side by side in a long, narrow shaft than by grouping them in a square shaft. In shallow mines separate shafts are often em ployed for hoisting and for pumping, ventilation and ladder-ways. One of the largest coal-mine shafts in America is situated at Wilkesbarre, Pa.; it is 1039 feet deep, 12 X 52 feet in size. and has five compartments. The methods of sinking mine shafts are essentially the same as those used in sinking shafts for tunnels. (See TuNxEr..) Slopes are openings begun at the outcrop of an inclined seam, which they fol low down into the earth. Slopes are usu ally made with three compartments side by side, two of which are used as hoistways and the third for the traveling-way, piping, etc. When the dip of the slope is under 40 degrees the slope is made about seven feet high, but when the dip exceeds 40 degrees cages have to he used and a great height is necessary. Slopes are usually lined with timber. Tunnels are nearly horizontal passageways beginning on the side of a hill or mountain and extending into the earth until they meet the coal-seam; they are built for both haulage and drainage purposes. and are con structed like railway tunnels, except that the cross-section is usually much smaller, and that it is lined with timber instead of with per• manent masonry. The forms of timbering used in coal-mining are various, and are of interest chiefly to the practical miner; special treatises should be consulted by those interested in the details. In a general way, it may be said that timber used for underground support in mines should be of a light and elastic variety of wood. Oak, beech, and similar woods are heavy and have great strength, hut when they do break it is suddenly and without warning, thus bringing disaster to the miners who might escape if a tough wood were employed which gives warning of rupture by bending and cracking. It is a very common practice to employ preserved tim ber in mining work. See FORESTRY.