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 burning coal, in order to reach the fire. When direct attack is no longer practicable, it is possible to extinguish the fire by sealing the mine workings, and exhausting the supply of oxygen. It is necessary, however, to keep the mine sealed until the burning timbers, or coal, and the red-hot rocks have become cool, or the fire will again break out. This sometimes requires two or three months. Where an effective sealing of the mine is impracticable it is sometimes possible to extinguish the fire from the outside of the mine by constructing a large reservoir or tank in the upper part of the mine-shaft and suddenly releasing a large volume of water by opening discharge-doors. The mass of water falling down the shaft is converted into spray, which is carried by the force of the fall long distances into the workings. Where the fire is in or near the shaft this method has proved very effective. Mine fires may sometimes be reached by bore-holes sunk for the purpose from the surface, and the burning workings below filled by flushing with culm and water. As a last resort the mine may be flooded with water. This is an expensive operation as it entails the cost of pumping the water out again and repairing the resulting damage. If the fire is in working places to the rise the water may not reach the burning portions of the mine, but will effectually seal them. But sufficient time must be allowed to elapse before pumping out the water, as otherwise the fire may break out again.

Mines may become flooded by the inrush of surface waters in times of great rainfall or sudden floods, or by the undermining of surface waters. The mine workings may also be flooded by large bodies of underground water. The surface floods must be provided with channels of sufficient size to carry them safely past the mine openings, and intercepting

ditches should be excavated for this purpose, and dams and embankments constructed to divert the flood waters. That it is possible to work with safety beneath rivers, lakes and even the ocean has been proved in numerous instances; mines in different parts of the world having been extended long distances under. the sea. In such cases preliminary surveys should be made to determine the thickness of rock over the proposed workings. Under favourable conditions mining may be conducted under the protection of a few yards of solid rock only, as in the submarine work for the removal of reefs in the harbours of San Francisco and New York. At Silver Islet, Lake Superior, mining was successfully carried on for years under the protection of a coffer dam and an arch of rich silver ore less than 20 ft. thick. At Wheal Cock near St Just in Cornwall the protecting roof was so thin that holes bored for blasting more than once penetrated to the bed of the ocean, and wooden plugs were kept on hand to drive into such holes when this occurred. In storms the boulders could be heard striking each other overhead. When large areas are undermined, as in submarine coal mining, it is best to have several hundred feet of protecting rock. In Great Britain the law requires that the workings shall be protected by 120 ft. of solid strata. When the presence of underground bodies of Water is known or suspected, advance bore-holes should radiate from the end of the advancing working place so as to give warning of the position of the body of water, these holes being of such length as to ensure a safe thickness of solid rock.

The caving in of mine workings results from the excavation of large areas supported upon pillars of insufficient size. While the mine workings are small the overlying rocks support themselves and the full pressure does not come upon the mine pillars. As the workings increase in size the pillars support an increasing weight until finally they are strained

beyond the limit of elasticity. When this occurs, the pillars begin to crack and splinter with a noise like musketry firing, and the roof of the mine shows signs of subsidence. This may continue for weeks before the final crash takes place. At first a fall of the roof occurs locally, here and there throughout the mine, and these falls may succeed one another until the settlement of portions of the roof has so far relieved the strain that the remaining areas are supported by the stronger pillars, and by the fallen rock masses. While abundant warning of the caving-in of the workings is thus given in advance it may happen that men are unexpectedly imprisoned by the closing of the main passage ways. The caving-in of the mine, however, is rarely so complete that avenues of escape are not open. In many cases, however, it has been found necessary to reopen the mine through the fallen ground, and even to excavate openings through the solid mineral. The history of mining is full of dramatic episodes of this character.

Accidents from the misuse and careless handling of explosives are unfortunately too frequent in mines. The conditions under Accidents which explosives may be stored, handled and used are carefully formulated in the mining laws of most states, but it is almost impossible to secure obedience to these regulations on the part of the miners, who are, as a rule,

both careless and reckless in their use of powder. In some states it has become necessary to provide for fines and even imprisonment of men disobeying the regulations regarding explosives.

Mine Hygiene.—While mining is not necessarily an unhealthy occupation, miners are subject to certain diseases resulting from vitiated air, and from unusual or special conditions under which at, times they are forced to work. Recent investigations have shown an alarming increase in mortality from miners’ phthisis in Cornwall, South Africa and elsewhere. This seems to be due to the dust abundantly produced in mining operations, and especially by machine drills when boring “dry” (rising) blast holes. Drill runners, who are compelled to breathe this dusty air daily, furnish most of the sufferers from phthisis. The increased mortality seems to be due to the general tendency toward forced speed in development work, which is secured by rapid drilling, and by an increase in the number of machine drills used in a single working-place. The miners, to save time, often return to their work after blasting before the powder-smoke and dust have been sufficiently removed. It is probable that the carbon monoxide seriously affects the general health and vitality of the men, and renders them more likely to succumb to phthisis. More effective ventilation will materially lessen the death-rate. In the metal mines of Cornwall and Devon special rules are now in force requiring the use of water in drilling, and other precautions. to lessen this danger from dust. In some mines dust seems to have but little effect on the health of the miners; indeed it is even claimed by some that coal dust decreases the mortality from phthisis. On the other hand, as in mining ores containing lead, arsenic and mercury, the dust may be poisonous. The climbing of ladders from deep mines not only lessens the efficiency of the men by reason of fatigue, but often tends to increase the mortality from diseases of the heart. In cold climates men coming from the warm atmosphere of a mine, often in wet clothing, are liable to suffer in health unless proper provision is made for the necessary change of clothing. In such cases the establishment of dressing-rooms, properly heated, and connected with the mine by covered passages will be necessary. These “change-houses” are provided with washing and bathing facilities, and arrangements for drying wet clothing. (q.v.) is a disease which finds a congenial habitat in the warm damp atmosphere of mines. and has become a veritable scourge in some mining regions. The disease yields readily to treatment, but is difficult to eradicate from a mine without stringent sanitary regulations to prevent its spread. The care of the health of the working force should be entrusted to competent mine physicians, thoroughly familiar with the conditions under which the miners work, and with the special diseases to which they are subject. The men should be instructed in the laws of sanitation, and in the proper care of injured men.

Mine Law.—Mine law is that branch of the law of real property relating to mineral and mining rights as distinct from rights pertaining to the surface of the ground. Under the common law the owncr of the surface possesses all mining rights as well, unless these have been reserved by some previous owner of the property. From very ancient times deposits of gold and silver have in most countries been held as the property of the crown. In public or government land the minerals as well as surface belong to the state, and not infrequently these rights have been separated by law and granted or otherwise disposed of to different owners. It is to the public interest that deposits of mineral should not be permitted to remain idle and undeveloped. This has been recognized from the earliest times, and laws have been framed in all countries for the encouragement of mining enterprise. In many cases the state or the ruler has sought to obtain a share in the profits of mining, or even to work mines for the individual profit of the ruler or of the state. But in most cases it has been found better policy for the state to divest itself of all interest in mining property, and to extend all possible encouragement to those who undertake the development of the mineral wealth of the nation. The mining laws of most civilized states grant the right of free prospecting over the public lands, protect the rights of the discoverer of the mineral deposit during the period of exploration, and provide for the acquisition of mineral property on favourable terms. Striking examples of the far-reaching effect of such laws is shown in the history of the Rocky Mountain region and western coast of the United States, the colonization and development of Australia, and the development of Alaska.

.—See C. Le Neve Foster’s Ore and Stone Mining (6th ed., London, 1905), or G. Köhler’s Lehrbuch der Bergbaukunde (6th ed., Leipzig, 1903). The following works may also be consulted: Books—Bertolio, Coltivazione delle minere (Milan, 1902); Brown, The Organization of Gold Mining Business (Glasgow, 1897); Brough, Mine Surveying (12th ed., London, 1906); Bulman and Redmayne, Colliery Working and Management (London, 1896); Colomer, Exploitation des mines (Paris, 1899); Curle, The Gold Mines of the World (2nd ed., London, 1902); Demanet, Traité exploitation des mines de houille (2nd ed., Brussels, vols. i and ii. 1898, vol. iii. 1899); Denny, Deep Level Mines of the Rand (London, 1902); Galloway, Lectures on Mining (Cardiff, 1900); Habets, Cours d’exploitation des mines (2nd ed., Liége, vol. i., 1906, vol. ii. 1904); Hatch and Chalmers, The Gold Mines of the Rand (London, 1895); Haton de la Goupillière, Cours d’exploitation des mines (2nd ed., Paris, vol. i. 1896, vol. ii. 1897); Hoefer, Taschenbuch für Bergmänner (Leoben, 1897); Hughes, Coal Mining (4th ed., London, 1900); M. C. Ihlseng, A Manual of Mining (4th ed., New York, 1905); Kirschner, Grundriss der Erzaufbereitung (Leipzig and Vienna, vol. i. 1898, vol. ii. 1899); Lawn, Mine Accounts and Mining Book-keeping (London, 1897); Lupton, Mining (3rd ed., London, 1899); T. A. Rickard, The Sampling and Estimation of Ore in a Mine (New York, 1904); Truscott, The Witwatersrand Goldfields—Banket and Mining Practice (London, 1898; G. F. Williams, The Diamond Mines of South Africa (New York;