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LEFT MINING 246 MINING ENGINEERS full length the broken-down coal is all removed. Later when the breasts in one section of the mine are all worked out the sustaining pillars between them are "robbed" or removed, allowing the roof to fall. In working metalliferous veins horizon- tal galleries termed "levels" are driven by the lode usually 50 to 100 feet apart. They are rarely perpendicularly above one another, as they follow the incli- nation of the vein. The levels are con- nected by means of small shafts, termed "winzes." Represented on a vertical plane, the vein will thus be seen to be cut up into pillars which are worked by the method of "stoping." In underhand stoping, the ore is gradually worked away downward from the floor of one level, the ore and worthless mineral be- ing taken out through the level next be- low. This method is especially adapted for working any valuable ores, as the loss is small. The overhand method, in which the miners stand on timber plat- forms and break down the mineral above them, is more economical, so far as cost of excavation is concerned; but the loss of ore is greater than by under- hand stoping, and hence it is best adapted for the working of low-grade ores. Placer Gold-Mining. — Many deposits of gold ores, as those first worked in Cali- fornia and those of the Klondike, are in the gravel or sand in the present or ancient stream beds. Such deposits are called "placers." In working these de- posits in the beds of existing streams, the course of the stream may be de- flected by a dam and sluice, and the water of the stream utilized for separat- ing the gold from the gravel which may be dug from the sti'eam bed. In the case of larger streams, mechanical dredges re- move the material from the bottom, which after separation of the gold is re- turned to the stream bed. In the old placers which are abandoned stream courses, generally above water level, hydi'aulic mining is resorted to. A stream of water from 6 to 12 inches in diameter and under the pressure caused by a head of several hundred feet is di- rected on the hillside where the old placer outcrops and rapidly washes it away. The material thus removed is sorted by the same water and the gold separated. The progressive legislation in connec- tion with mines has proved beneficial in diminishing the proportion borne by the accidents to the number of miners em- ployed. Great improvements have re- cently been made in sinking shafts, safety lamps, underground haulage. coal-cutting machinery, worked by com- pressed air and electricity, and pump^ ing apparatus. Better methods of sort- ing, picking, and washing coal have been adopted. Good progress has also been made in the application of steel girders as props and bars, and in reduc- ing the cost of coal consumed at col- lieries. By means of forced draught and better mechanical stoking much coal practically unsalable has been utilized to great advantage. But by far the most appreciable good that has been done in connection with mining in recent years has been the scientific investigations carried on by the Bureau of Mines {q. V.) respecting the causation and preven- tion of explosions in coal mines, and im- proved means recommended and adopted to diminish, if not minimize, these dis- asters, where many lives have been lost and much valuable property has been destroyed. In England and Ireland the crown has the right to all mines of gold and silver; but where these metals are found in mines of tin, copper, iron or other baser metal, then the crown has only the right to take the ore at a price fixed by statute. In Scotland gold mines belong to the crown without limitation, and sil- ver mines when three-halfpence of silver can be extracted from the pound of lead. As a general rule, in the United States as well as in Great Britain, whoever is the owner of freehold land has a right to all the mines underneath the surface, for his absolute ownership extends to the center of the earth; but under special grants and contracts it is not uncom- mon for one person to be owner of the surface of the land and another to be owner of the mines beneath; or several persons may be owners of different kinds of mines lying one above the other in dif- ferent strata. On the public lands of the United States, a title or license may be obtained by any citizen from the gen- eral land office at Washington, at the rate of $5 per acre of surface pre-empted. MINING ENGINEERS AMERICAN INSTITUTE OF, association established in 1871, having among its objects the development of the arts and sciences as- sociated with the mining of minerals and metals and their uses in trade, and the publication of information connected with the industry and profession. The institute has its central offices in New York City and issues several publica- tions in the course of the year, including the "Annual Transactions," and a month- ly "Bulletin." It holds periodical meet- ings and has a membership approaching 6,000.