Page:The American Cyclopædia (1879) Volume V.djvu/74

 70 COLLIERY The natural decay of wood unfits it for use in pits. But the chief defect is in the form of the pit, and the English mining engineers long since discovered this serious objection to square or oblong pits, and substituted the round pit, FIG. 14. Pennsylvania Anthracite Shaft (section). a, pump and rods ; &, pump apartment ; c, c', hoisting apart- ments ; d, travelling apartment ; <?, ladders. 1, 1, support- ing timbers ; 2, pump timbers ; 3, 3, 8, dividing timbers ; 4, backing plank. in which brick, stone, or iron can be economi- cally used to secure the sides of the shafts. Besides, this seems to be the only sure method of damming back the water, which in the tim- bered pits is allowed to enter the shafts and must consequently be pumped out at constant expense. But in circular pits all the water above the coal, and particularly the more abundant surface drainage, which is most seri- ously felt in the upper 300 to 500 ft., is dammed back with masonry or iron tubing. As the surface drainage always varies considerably in wet and dry weather, a portion of the pit is sometimes wet and sometimes dry, and this alternation, with the incident changes of tem- perature, induces decay when the pit is tim- bered, and replacement is dangerous and diffi- cult. The great size of the Pennsylvania an- thracite pits is the natural outgrowth of the great size of the coal beds. Nine tenths of the anthracite mines are from beds varying from 10 to 30 ft. in thickness. Mine cars of great size and of unwieldy proportions are used in many of them, with doubtful economy, since the most available systems of mining, known as bord and pillar and longwall, cannot be properly followed in steep-dipping beds with cars of greater capacity than one ton of coal each ; yet the cars used in the anthracite mines generally contain from one and a half to three tons of coal, and weigh with their contents as much as five tons. They cannot be taken up the steep pitches by mules or be handled by the men ; and this involves a second handling of the coal and some contrivance for getting it from the mines to the cars, which cannot leave the levels or gangways. Shutes are commonly used, but when the dip is too steep to admit the use of mules to draw the cars up to the mines, and too low for the coal to slide down a shute, great trouble and expense are involved. Besides, these systems of breast and pillar or post and stall mining are defective in many other respects. Some of the large an- thracite pits are capable of producing 1,000 tons of coal per day ; yet this has rarely been accomplished, from the difficulty of handling so many heavy cars at the top and bottom of the pit, or the greater difficulty of getting them to the bottom of the pit through a single level or double gangway, one on each side of the pit, to which the system in use, and the neces- sity of working the larger beds only, confine most of the anthracite mines. But this pro- duction is exceeded by much smaller and deep- er English pits, in which cars or bogies hold- ing from 8 cwt. to one ton are used. In some of these deep pits a regular production of 2,000 tons per day is not unusual, though 250 to 500 tons is more common. The late mining laws both of England and Pennsylvania require two openings for ingress and egress to each mine, so as to secure the safe retreat of the workmen in case of accident, and more perfect ventila- tion. Some of the most serious and fatal acci- dents have been occasioned by the absence of a second outlet ; one of the most notable was -< ^'T 3 3 i C 1 3 C r '2 2-' 3 FIG. 15. English Circular Shaft. a, pump way ; &, travelling way ; c, c', hoisting ways ; eZ, brick or stone lining ; e, rock. the Avondale disaster, in the Wyoming valley, near Plymouth, Pa., in 1871. This was oc- casioned in all probability (though the fact was never established) by the exceeding dry- ness of the timbers in the upcast portion of the pit, which was divided by a partition of wood. One portion of the pit was used for hoisting coal and the admission of air, and the other for the egress of the mine vapors. At the bot- tom of the latter a furnace was in constant use, the heat from which made the timbers like tinder, and the soot could not fail to ac- cumulate, as in ordinary chimneys. A spark only was necessary to ignite the one or the other. But in other cases, the burning of the structures erected over the pit's mouth, the destruction of a portion of the pit by explosion or caving, flooding of the mine by water, or the derangement of machinery, all point to the necessity of a second outlet from each mine, as a matter of common prudence. The methods of descending and ascending deep pits have been and still are very generally defective and