Mine, an excavation made in the earth for the extraction of minerals. When the material to be extracted is a rock of any kind, the excavation is known as a quarry. We find very little in classic literature that gives any real information about the mines of antiquity or the manner in which they were worked. It is certain, however, that the Phoenicians and Egyptians at the earliest periods of history had an abundance of metals. The Phoenicians obtained from Sardinia and from other islands of the Mediterranean gold and iron, as well as other metals; they are known to have mined in Spain, probably for lead and silver, and to have traded with the Britons for the tin ore of Cornwall and Devon. Of even greater antiquity was the mining of the Egyptians, who had mines of copper, silver, and gold in productive operation, both on the Ethiopian and the Arabian border. The Sinaitic desert con-tains'the ruins of mining works, probably executed by the Egyptians. Abraham found gold and silver in use among them. In the time of Alexander gold, silver, copper, and iron were obtained in Ethiopia, and iron, at least, in Libya. India and Caramania (modern Kerman) produced gold, and the latter country also silver and copper.

In Asia Minor the gold mines formerly owned by Croesus were worked down to the time of Xenophon, but Strabo says that in his day they were exhausted. There were iron mines and skilled workmen in Palestine. Ancient writers speak of rich gold and silver mines in Arabia Felix, no traces of which remain. The Athenians worked rich silver mines in Attica and gold mines in Thrace and Thasos. Thessaly produced gold, Boeotia iron, and Epi-rus silver. Before the time of the Romans mining was carried on in many parts of western Europe. The Etruscans and the Sabines in Italy were acquainted with copper, and the former discovered iron in Elba. The northern tribes of Italy obtained gold by washing; the tribes of Gaul are known to have mined for gold, silver, copper, and iron; and in Spain and Sardinia extensive and productive mines were established by the Carthaginians. Britain produced gold, silver, iron, lead, and tin. After the conquest of Caesar, the tin of Cornwall was shipped first to the Isle of Wight, and thence to the coast of Gaul, where it was loaded upon horses and transported to Marseilles, a journey of 30 days. The early Romans did not work the mines of their native land.

The first two Punic wars delivered into the power of Rome the important mines of Sardinia, Sicily, and Spain. Subsequent conquests added those of Asia Minor, Macedonia, and Greece, and still later the remaining mines of western Asia and those of Egypt were acquired by the armies of Pompey and Augustus. Those of Gaul yielded to Caesar. The tin mines of Britain' were their latest conquests of this sort, and Koine was then mistress of all the important mines of the ancient world. Under the republic the mines were worked by lessees, who employed numbers of slaves, and ibjected the mineral deposits of the provinces to rapid and reckless robbery. During the period from the first Punic war to the empire there was an immense production of metals, and many of the mines were exhausted. The emperors established governmental supervision, and worked the mines through regularly appointed officials. Mining in the countries belonging to the West Roman empire declined rapidly from the 3d century, and after the 5th it ceased entirely.

The Byzantines gradually surrendered their mines to the Arabs; those of Asia Minor, Thrace, and Greece were the last which the eastern empire retained. - Mining is known to have been carried on at Andreas-berg in the Hartz since the year 908. The-famous Rammelsberg mines were discovered in 972 by the pawing of a steed named Ram-mel, tied to a tree in the forest. The Freiberg district was discovered about 1165, and has been steadily worked since 1547. Traces of ancient mining in the United States are confined to the copper region of Lake Superior, and to certain districts in New Mexico. In both cases the implements seem to have been rude hammers of stone. In New Mexico there is a large excavation known as the Turquoise mine, from which a trachytic rock, carrying turquoise in seams, has been laboriously extracted by a race of whom not even a tradition now exists. In ancient times muscular force, assisted only by applications of fire and occasionally by the power of water, was the miners1 resource. A most suggestive picture of rude mining operations is given in the book of Job, xxviii. 1-11, of which Conant's translation brings out the beauties very strikingly: "For there is a vein for the silver, and a place for the gold, which they refine.

Iron is taken out of the dust, and stone is fused into copper. He puts an end to the darkness; and he seaarches out, to the very end, stones of thick darkness and of death-shade. He drives a shaft, away from man's abode; forgotten of the foot, they swing suspended, far from men! The earth, out of it goes forth bread; and under it is destroyed as with tire. A place of sapphires are its stones; and it has clods of gold. The path, no bird of prey has known it, nor the falcon's eye glanced on it; nor proud beasts trodden it. nor roaring lion passed over it. Against the flinty rock he puts forth his hand; he overturns mountains from the base. In the rocks, he cleaves out rivers; and his eye sees every precious, thing. He binds up streams that they drip not; and the hidden he brings out to light." Pliny ("Natural History," xxxiii., 4) gives a similar description of shaft-sinking operations: "Elsewhere pathless rocks are cut away, and are hollowed out to furnish a rest for beams. He who cuts is suspended with ropes. . . . For the most part they swing suspended, and fasten up lines for a pathway.

They go where there is no place for the footprints of man." The removal of surface material by sluicing was also practised in ancient times in Spain. - The operations of mining may be comprised under four heads: 1, the discovery of mineral deposits and the testing of their value; 2, the establishment of access to such deposits; 3, the extraction of the mineral; 4, the protection of the works and workmen.

I. Discovery And Testing Of Mineral Deposits

For a description of the modes of occurrence of the rocks and minerals which are objects of mining, see Mineral Deposits. The presence of such deposits is indicated by various signs. Sometimes the veins themselves, if harder than the enclosing rocks, crop out at the surface unaltered. More frequently the outcrop is indicated by decomposed rock, which when ferruginous is called "gossan." Loose pieces of gangue and ore, known to western miners as "float quartz," and found upon the surface and in the soil, frequently lead to the discovery of veins. The lead miner of the limestone districts of the Mississippi valley is guided by depressed lines upon the surface, indicating the existence of fissures. The magnetic needle is employed in the discovery of certain ores of iron, and the ancient superstition of the divining rod for the discovery of hidden springs and mineral veins is not yet extinct even in this country. (See Divining Rod.) When the neighborhood of a mineral deposit is suspected and no certain indication of its exact locality appears, it is sought by prospecting pits, cuts, drifts, or borings. Prospecting pits are commonly dug upon the supposed outcrop of a deposit, to test its dimensions and quality.

Open cuts are usually run on the surface at right angles to the prevailing course of the veins of the district, and are excavated down to the solid rock for the purpose of exposing the veins which they may cross. This is called " costeening." Boring is employed for determining the character of rock strata, and the position of mineral deposits in them. It has been usually applied to coal beds or to strata containing salt or petroleum deposits. In the latter cases the bore-boles subsequently serve for the extraction of brine or oil. The invention of the diamond drill (see Boring), by means of which holes can be driven in advance horizontally for hundreds of feet, has greatly enlarged the applications of boring as a means of exploration. Horizontal adits, or crosscuts, driven into the sides of hills at right angles with the veins known to exist in them, are the surest but most expensive method of exploration. It may be resorted to when the existence and value of the deposits are well known, and the topography is such that the entry may subsequently be valuable for drainage and transportation.

Finally, new deposits may be discovered under ground by driving experimental openings from mines already in operation. - The value of deposits is tested by shafts and drifts, usually excavated within the deposit itself. The construction of such works in the barren rock is seldom undertaken until the vein is found to be worthy of the expenditure. In the case of coal, building stone, iron ore, and, in general, all materials which occur in extensive and tolerably uniform deposits, and the value of which is small in comparison with their bulk, the test of quality is not difficult. But minerals of more concentrated value usually occur mixed with such variable proportions of "gangue" or barren matter, and when in fissure veins are subject to such variations in width and course, as to render it necessary to expose considerable bodies of vein matter, and to make tests either by thorough sampling or by actual reduction of large quantities, before the economical value of the deposits can be ascertained. By connecting with the shafts or inclines sunk upon the dip of the vein longitudinal drifts run upon its course, this object can be measurably secured.

Alluvial deposits, such as those of gold and stream tin, are tested by actual working with pan, sluice, etc. "When large operations, like those of hydraulic mining, are contemplated, the body of earthy gravel, cement, etc, if its value is not already known, is tested by shafts sunk to the bed rock at a sufficient number of points to give an indication of its average contents.

II. Approaches To Mines

Access to mineral deposits for permanent exploration is established, first by suitable wagon or tram roads on the surface, and secondly by either stripping the overlying soil and rock from the deposit itself, as is done in quarries, clay banks, and some iron mines, or by sinking a shaft or running a drift or crosscut from the surface into the deposit. In the case of beds or veins which dip at a convenient and uniform angle, the shaft may be carried down upon the deposit itself, and is then usually called a slope or an incline. For less regular deposits, and for those in which the angle of inclination is inconvenient or variable, or the vein matter is too valuable to permit the leaving of it in pillars to protect the shaft, it is better to drive a vertical shaft at some distance from the outcrop, in the hanging wall, so as to strike the vein at a considerable depth. A gallery run from the surface in a nearly horizontal line, to effect access and drainage, is called an adit or entry, and in some situations, as at the base of steep hills, this may be made the principal feature at the mine, the main workings being carried on through it until the vein is exhausted above its level. Sometimes the nature of the shafts permits the opening of mines at different levels, by means of adits.

This system was most highly esteemed before the improvements in machinery and the introduction of steam favored the economy of mining in deep shafts. When adits must be driven for long distances through hard and barren rocks, it is sometimes difficult to decide whether the cost of their construction will be repaid by the saving in hoisting, drainage, and mechanical ventilation. Adits are usually called tunnels by miners of the Pacific states and territories, but this is a misnomer, as a tunnel proper extends entirely through a hill. Mining shafts are generally rectangular in section, and range in size from 3 or 4 ft. to 6 ft. on the shorter sides, and from 6 ft. to 20 ft., or even more, on the longer sides. This form facilitates timbering, and at the same time permits the best utilization of space, through the division of the shaft by partitions into separate compartments for pumps, hoisting, ladder ways, etc. Adits are placed with reference to securing the greatest depth below the surface by running as short a distance as possible, particularly in barren rock; with reference to the presence of a good place for a "dump " at the adit mouth; and also with reference to easy escape of waters, freedom from flooding by freshets, and facility of natural ventilation when the adit is to be connected with a shaft.

For the latter purpose it is well that the adit mouth should not be in a narrow ravine or in the corner of a valley. Dimensions of adits depend upon the amount of water expected to run in them and the other purposes to which they are to be put. When in barren rock, it is an object to make them as small as practicable; 7 ft. high and 5 to 6 ft. wide is a convenient size. But when transportation is to be carried on and double tracks are to be laid, the dimensions must be increased. The height of the adit available for passage is diminished by the water channel, which usually runs under the floor or in a ditch at one side. The grade of adits is determined with reference to the amount and character of the water flowing in them and the speed which it is desirable to give to the current. The ancient mining regulations of Prussia required of deep adits a grade of from 1 in 800 to 1 in 400. Some of the adits at the coal mines of Saarbriick rise at the rate of 1 in 1,600; others at the rate of 89 in 64,000. According to the Saxon law, the grade may vary between 3 in 10,000 and 1 in 1,000. The long Ernst August adit in the Hartz has, for a length of nine miles, an average grade of 0.67 in 1,000. Here the water in the adit is itself used for transportation, and the current is intentionally kept slow.

Access is further obtained to the different parts of the mineral deposit by subordinate shafts and galleries excavated in the deposit. These interior shafts not extending to the surface are known as winzes, and usually serve to connect the galleries on different levels. The galleries are known as levels or drifts in vein mining, and gangways in coal mining. When a mine is opened by a vertical shaft, the vein is sometimes cut by a crosscut level run from the shaft through barren rock, at a point higher than the intersection of the shaft and the vein. From the point where the crosscut enters the vein, levels are then run in both directions horizontally on the vein. After the main shaft has reached the vein and has been carried through it, the distance between vein and shaft of course grows larger with increasing depth, and the vein must be again opened by crosscuts from the shaft at different levels. The levels opened in the vein are so many parallel roads on the vein, succeeding each other every GO to 100 ft. in depth. The winzes connecting them serve both in ventilation and in extraction, besides affording convenient access to different parts of the mine.

The running of drifts to make connection with old and abandoned workings is sometimes dangerous, when the old workings are full of water and their exact position is not known by surveys. In such a case the approach is made cautiously, and a bore-hole is kept in advance, to tap the accumulated waters in such a way as to avoid an excessive flow or give the workmen time to escape. An accident of this kind at the Gouley mine, near Aix-la-Chapelle, in 1835, which caused the drowning of 63 miners, gave rise to the publication by the government of the Khenish province of exact regulations, which constitute an excellent guide to the mining engineer.

III. Extraction Of Minerals

To perform the work of regular extraction with due economy and safety, the following circumstances must be considered: the shape of the deposit, as a tabular or sheet deposit, a mass or stock work, regular or irregular, etc., and if a tabular deposit, like a fissure vein or a bed, then its course and dip, its folds, basins, faults, and breaks; the thickness and inner structure of the deposit, or, in ore veins, the nature and distribution of the ore bodies, the amount of barren gangue, and in coal beds and other deposits the proportion of marketable to waste material; the character of the "country" or wall rock, as making a solid or a precarious roof, and requiring more or less support; the number, relation, and distance apart of several deposits which it may be desirable to work at once or successively, as for instance scams of coal, lying one under the other; the conditions of ventilation, particularly where explosive gases are to be feared; the conditions of drainage; the character, abundance, and price of materials for under-round supports (timber, masonry, iron pillars, loose rock, or earth); the size and shape of the pieces of material to be extracted (commercially important in coal and quarried stone); the method of excavation to be employed (picking, shovelling, fire setting, hydraulic sluicing, leaking, blasting, etc.); and finally, in a subordinate degree, the nature of the mineral itself, as for instance very rich and brittle silver ore, which is liable to be lost in line particles among the piles of waste, or some kinds of coal which deteriorate by standing too long in the mine after they have been exposed and drained, or clays which become like quicksands in contact with water.

Any one of the foregoing conditions may, under certain circumstances, be decisive as to the choice of a method of extraction. - Hydraulic mining is an application of the power of water, under high pressure and at great velocity, to move great masses of material, separate the heavier and more valuable portions, and convey away the lighter waste. (See Gold Mining.) In its modern form it was invented in California about 1852, and is mainly employed in that state. It has been introduced at Iron mountain, Missouri, for the purpose of removing and concentrating the surface ore of that locality. For hydraulic mining, it is necessary to have, besides a deposit suitable to operate upon, a supply of water at a proper latitude, and an escape for the turbid stream, at a level below all the workings. The waste material is thus removed by the current at small cost, while the gold is precipitated to the bottom and caught in crevices,. " riffles," etc. As most "hydraulic-gravel " deposits have been accumulated in basins of ancient river channels, they are surrounded by hard rock, called "bed rock" below, and "rim rock" where it comes to the surface at the edge of the deposit.

For hydraulic exploitation, the bottom of the deposit must be underrun by a tunnel through the bed rock, and a short shaft from the overlying deposit must be connected with this tunnel. Then the bank may be " hydraulicked " down, and everything except the large bowlders sluiced into the shaft and tunnel, and so away to lower grounds. The method of extraction by leaching is peculiar to certain rock-salt mines, in which the mineral is too much mixed with earthy and stony matter to be quarried. Chambers are excavated in the mass, and filled with water, which is allowed to stand until it has extracted from walls and roof sufficient salt to render it a concentrated brine. It is then drawn off, and conveyed in pipes to the boiling works. A layer from the roof of the chamber, disintegrated to a certain distance by this leaching, falls, covering the floor with material from which the salt has been extracted, and leaving a new roof exposed for a repetition of the process. Thus the chambers slowly rise through the mountain.

This method is in use at Berchtesgaden in S. E. Bavaria, and Hal-lein in Salzburg. - Other modes of extraction are divided into two classes: those in which the space excavated is refilled wholly or partially with waste material, and those in which no such " packing" or " gobbing up " is employed. The former class is subdivided, according to the direction in which the work proceeds, into overhand stoping, underhand stoping, cross stoping, and long-wall working. (The latter method and its modifications, used chiefly in coal mining, where the seams are not too thick, steep, or variable, may be employed either with or without gobbing up.) The word stope is probably a corruption of step, and refers to the stair-like appearance presented by the face of the excavation. Overhand stoping is conducted as follows: From the level below the ground to be exploited, a "raise " or upward shaft is driven up into the ground, and from this the different " breasts " are driven horizontally on the vein, in one or in both directions. The extraction begins at the bottom, by the excavation of a block having the width of the vein, a height of 4 1/2 to 9 ft., and a length of not less than 7 nor more than 30 ft.

In this work two sides of the rock are always free: the upright face, toward the central shaft, and the lower horizontal side, over the level. When the breast has been driven far enough, a new workman or set of workmen may begin with a second breast, while the former still continues to advance. Fig. 1, representing the profile of a double stope, shows the order in which the work proceeds. The space behind and below the workmen is filled up with the waste rock, broken from the vein in order to get at the ore, or with rock brought from elsewhere for this special purpose. Openings or "chutes" are left in this, through which the ore can be allowed to fall to the level below, where it is received in cars. This level is usually protected by a roof of stulls and lagging, on which the waste rock is piled, as is shown in fig. 2; or a portion of the vein is left standing over the level, as a protection. The workmen stand on the waste rock, and stoping goes on in the manner indicated, until the whole of the valuable mineral between the bottom level and the one next above (say 60 to 100 ft., measured on the dip of the vein) has been extracted.

Of course, by starting stopes at different points on the lower level, within the limits of the mining claim, or the body of valuable ore, more men can be set at work. But the regular productiveness of a mine is not susceptible of indefinite increase in this way. The maximum rate of exploitation which can be maintained until the mine is entirely exhausted, depends upon the rate at which the shaft or shafts can be sunk and new levels opened at greater depths. The too rapid exhaustion of one level would necessitate a suspension of active extraction while the next level below was in course of preparation; and in this work of sinking shafts and running drifts (sometimes called the "dead work" of the mine) it is not possible to multiply the number of men, so as to secure more rapid progress. Only so many men can be accommodated at the bottom of a shaft or the end of a drift; and when their effectiveness has been raised to the highest point by selecting good workmen, dividing them into three "shifts" or gangs, working eight hours each in turn, employing the most suitable tools and explosives, and, if circumstances are favorable, drills operated by steam or compressed air, the limit of practicable progress has been reached; and this determines the normal productiveness of the mine.

Driving the stopes faster than the dead work is "robbing" the mine. Underhand stoping is the reverse of the method just described. Here the stopes begin from the level above, and may be commenced (if the presence of water is not too troublesome) before any lower level has been opened. The ore has to be hoisted, and the waste rock has to be lifted by hand and packed on stalls behind the miner, as shown in fig. 3. This system permits an earlier beginning of extraction, and gives the workman a firm footing on the solid vein and an easier and safer direction of working (viz., downward instead of upward). Moreover, there is less chance of losing small pieces of rich ore, which in overhand stoping get into the waste rock under foot and cannot he recovered. But overhand -toping has two great advantages: first, the convenience of rolling and dropping rock and ore, instead of hoisting them; and second, the saving of timber, which in most mining districts soon becomes expensive. The great amount of timber used in an underhand stope is not merely lost; it may give rise by its decay to slides in the packing, or the necessity of expensive repairs to prevent them.

Both overhand and underhand stoping are variously modified, as for instance in their application to any thick vein in which cross stoping is not desirable. In such eases, the vein is worked in successive layers or zones, parallel with the walls, each layer beginning with that on the foot wall, being stoped out by itself, as a separate vein; 12 ft. is usually as great a thickness as can be stoped at one time with safety or convenience. Cross stoping is common in working thick veins. In this method, the vein material is removed in layers, not parallel with the walls, but extending from the foot to the hanging wall; and in each layer the exploitation takes place by driving breasts across the vein, leaving pillars between them; supporting the roof of the breast, (J to 12 ft. wide, with timbers until it has reached the hanging wall; then withdrawing the timbers and packing the excavation with waste rock; and then extract-ing the pillars and replacing them also with waste rock. A cross layer of the vein, 6 or 7 ft. in vertical height, having been thus removed and the space packed, the operation is repeated with the layer next above. Fig. 4 shows this method by a vertical cross section.

It is employed at the quicksilver mine of Idria, Carniola, and in various modifications at the zinc mines near Aix, the coal mines of Le Creuzot and St. Etienne, in France, the mines of roofing slate near the Rhine, and the lignite mines in Lower Styria. Long-wall working is employed on nearly horizontal deposits, usually coal beds. It may be classed as retreating or advancing, according to whether the extraction begins at the borders of the field or section of the bed to be worked, and retreats toward the main shaft, or begins at the shaft and advances toward the limits. In the latter case roadways are kept through the ground already worked out. Varieties of this method are employed in the copper schist beds of Mansfeld, and at many foreign coal mines. - The methods of extraction without packing are: those in which the roof or hanging wall is supported by timbering, masonry, or pillars of the original material, left standing until the workings are to be abandoned; and those in which the roof is allowed to come down immediately after extraction. In the mines of the Comstock vein in Nevada, the spaces are kept open with elaborate timbering, framed as for immense houses. This is a great expense, besides being a source of loss and danger in case of fire.

A conflagration in the Yellow Jacket, Kentuck, and Crown Point mines on that lode, which began April 7, 1869, not only cost many lives, but continued to burn, from 600 to 900 ft. underground, for many months, being sustained by the great quantity of dry timber in the stopes. - The system of extraction by breasts or chambers and pillars is practised chiefly in coal mining. It is wasteful of coal, since the pillars of that material left standing are but partially recovered by "robbing," when the breasts are worked out. It is estimated that from 30 to 40 per cent, of the coal in the anthracite mines of Pennsylvania is thus lost. - To the department of extraction belong also the various methods of transporting workmen and material. Where an adit or a slope of gentle inclination leads to the underground workings, the ore and rock are brought out in cars or wagons. For horizontal transportation men or boys, horses, mules, stationary engines, and locomotives are employed. Hoisting through shafts is performed by windlass, horse whim, or water or steam power.

When the material extracted has to be lowered, as for instance to deliver it from breasts or stopes to the main roads of transportation underground, or from the shaft or adit mouth to a loading place at a lower level, gravity tramways may be employed, on which the loaded cars, descending, pull up the empty ones. The entrance and exit of workmen through shafts is effected by ladders or stairs, or by lowering and hoisting them in cars, buckets, or cages, or by means of an ingenious arrangement called the man machine or Fahrkunst. Whatever method is adopted, every mine should be provided with ladders in good repair, since other means may fail at a critical moment. In its simplest form, the fahrkunst is a continuous piece of wood, iron, or wire rope, extending from the top to the bottom of the shaft, and provided at regular intervals (8 to 24 ft.) with small platforms, upon which a miner can stand. This frame is so placed in the shaft, and supported by counter weights (and, in inclined shafts, friction rollers), that a regular reciprocating motion, like that of the pumping rods, can be imparted to it.

The machinery is so arranged that the stroke is exactly half as long as the distance between the platforms on the fahrkunst, and at the end of the stroke in each direction there is an instant's pause. During this instant the miner can step from the machine upon a fixed platform in the side of the shaft. As the fahrkunst is kept constantly running, a miner wishing to ascend by means of it has only to step upon it as it begins an upward stroke, step off at the end of that stroke, wait until the down stroke brings opposite to him the platform next above, then step upon that, and be carried another lift higher. At the same time, another miner may descend upon the same machine, by stepping on for the down stroke, and waiting during the up stroke. The double fahrkunst has two such frames or rods, running reciprocally side by side; and here the miner steps across from one to the other, always finding opposite to him, as the platform on which he stands pauses in its movement up or down, a platform on the other frame, just about to commence its movement in the same direction. The moving platforms are usually small, holding but one person conveniently. When two miners pass each other, one steps upon a ladder placed between the two frames.

In Belgium the moving platforms are so large as to fill the whole shaft, and take several workmen at a time. The rate of working may be seen from the following statement, calculated for a shaft of 800 ft.:

Double Overhand Stope.

Fig. 1. - Double Overhand Stope.

 Single Overhand Stope, packed with waste rock.

Fig. 2. - Single Overhand Stope, packed with waste rock.

Underhand Stope.

Fig. 3. - Underhand Stope.

Cross Stoping.

Fig. 4. - Cross Stoping.

FAHRKUNST.

Stroke.

Double strokes per minute.

One man descends in

500 men in

Ordinary double..

10 ft.

5

8 m.

1 h. 47 m.

Swift "

10 "

10

4 m.

54 m.

Large Belgian...

10 "

5

8 m.

27 m.

The Belgian machine is here assumed to be carrying four men on each platform. On ladders one man usually descends 800 ft. in about 30 m., and ascends in an hour. The time allowed for 500 men is about 2 1/2 hours to descend and 5 hours to ascend. The waste of strength involved is also to be considered. When miners are hoisted in the cages, the average velocity being about 15 ft. per second, and the average load four men, about 3 1/2 hours are required to lower or raise 500 men in a double vertical shaft of 800 ft.; or when the load is six men, 2 1/2 hours. At the Comstock mines, Nevada, 12 men descend at once, at a rate varying from 400 to 800 ft. per minute. Some of these mines are more than 1,600 ft. deep.

IV. Protection Of The Works And Workmen

Arrangements for the protection of the miners and works include timber or other supports, ventilation, and drainage. Shafts and permanent ways are carefully protected, if necessary, with stout timbering, masonry, or even cast-iron linings. Pillars of rock left standing, piles of waste material packed in the empty spaces, and posts, stulls, lagging, etc, suffice for stopes. In some mines the temporary supports are iron columns, or even screw-jacks, which can be removed without damage and used again. Ventilation is necessary to remove explosive and inflammable gases (car-buretted and sulphuretted hydrogen and carbonic oxide, which are also poisonous), and simply poisonous gases, such as sulphurous acid, carbonic acid, and quicksilver or arsenic vapors. Natural ventilation is secured by having two openings to the mine, at one of which (called the intake or downcast) fresh air enters, while the foul air escapes at the other (upcast). The difference in altitude between these openings, and the difference in temperature between the entering and the escaping air, determine the strength of the natural ventilation. It is likely in temperate climates that the air in the mine will be warmer in winter and cooler in summer than that outside.

Hence the draft will be in winter out through the highest opening, and in summer the reverse, while periods of stagnation will occur in spring and autumn. The natural draft may be assisted by wise choice of the localities for the openings, or by use of weather caps and chimneys over the upcast; but these aids are not effective except where the intake is an adit. Artificial ventilation is effected by increasing the difference of temperature between the entering and the escaping air, so as to render the currents comparatively independent of the weather, or by increasing mechanically the difference in density. In the first class of instances, either the escaping air is warmed, or the entering air is cooled; in the second class, either the escaping air is rarefied by suction, or the entering air is condensed by blowing. The escaping current may be warmed by connecting the upcast with the chimney of a steam boiler above ground, or with a special furnace above ground, or by means of a furnace in the shaft, or near the bottom of it, or by introducing steam jets into the shaft. The jets have a mechanical as well as a thermal effect; but the total effect per pound of coal consumed is less than that of the furnace.

The cooling of an entering current of air is sometimes effected by allowing water to fall into the downcast, and is also an incidental effect of the water blast or hydraulio bellows, a simple contrivance by which a falling stream carries a draft of air with it into a receiver, where the air is disengaged from the water, and forced, under a pressure due to the water column, into the mine. Ventilating machines (exhausting or blowing machines) are used almost exclusive-ly in coal mines, where a great excess of air, to dilute injurious gases, is a vital necessity. These ventilators are either reciprocal (pumps) or rotary (fans). The latter are generally employed, and for extensive ventilation the exhausting fans are usually preferred to the blowers. One of the most effective fans, Guibal's, gives, with a diameter of 14.34 ft. and 8 arms revolving 134 times per minute, a current of 929 cubic feet of air per second. The distribution of the air currents through the mine, so as to bring fresh air to the workmen, and remove all foul gases to the upcast, is very important, and requires a system of air courses, doors, etc.

Portable lights in mining are torches, candles, and oil safety lamps. (See Lamp.) Stationary lights are also employed (lanterns with oil or petroleum, gas light, and various electric lights) for illuminating permanent roadways, landings, etc. The drainage of mines is effected by natural means (through adits) or by means of pumps or bucket-. These are sometimes operated by hand or horse power or wind, more frequently by hydraulic engines, and most frequently by steam.

V. Mixing Laws And Schools

The inalienable right of the sovereign to the metals in the soil is an ancient doctrine, particularly with regard to the precious metals, but is gradually passing away in civilized countries, the governments of which are selling the "mineral rights" which they have hitherto farmed out or operated directly for the revenues of the state. A police supervision, in the interest of public safety and of political economy, is usually maintained. The laws of European states regulate minutely the privileges granted to miners, and their relations to the government and to the proprietors of the soil. In England and the United States, the title to the minerals beneath the surface usually goes with the ownership of the land, but may be disposed of by sale or lease separately. Gold and silver mines were excepted in Great Britain up to the time of William and Mary, being obliged to pay a royalty to the crown. On the public lands of the United States, citizens arc allowed to mine without royalty, according to the local regulations established by state and territorial legislation and by the citizens in each district, subject to the general mining laws passed by congress, which fix as the conditions of the possessory title or license a suitably recorded claim, and the performance of a certain amount of work annually.

A complete title, covering a surface tract, and the right to the mineral veins having their outcrops or apexes within the vertical planes bounding the Baid tract, together with the right to follow such veins in depth, though they may extend under the surface of adjoining tracts, may be obtained after survey and advertisement, by purchase from the United States, at the rate of $5 per acre of surface patented. The mining law is administered, like the agricultural land laws, by the commissioner of the general land office at Washington. In most civilized countries statistics are compiled annually by the government, showing the production of mines and metallurgical works. In the United States this is done imperfectly in. the decennial census, and has been done since 1866 for the states and territories west of the Rocky mountains, with particular reference to the gold and silver product, by a special commissioner of the treasury department. (For statistics, see the articles on the different metals and countries.) Regulations to secure safety of miners, and to determine the rights of mining operators toward each other and toward land owners, are made by the individual states and territories. - In European countries schools have long existed for training engineers and metallurgists for this industry.

Among the most celebrated are the mining academies of Freiberg in Saxony, Clausthal in the Hartz, Schemnitz in Hungary, Leoben in Styria, the academy at Berlin, the ecole des mines at Paris, and the royal school of mines in London. Much attention has of late been given to this subject in the United States, and the following institutions give special instruction in these branches: the school of mines of Columbia college, New York; the Rensselaer polytechnic institute, Troy, N. Y.; the Pardee scientific department of Lafayette college, Easton, Pa.; the Sheffield scientific school of Yale college, New Haven, Conn.; the Massachusetts institute of technology, Boston, Mass.; the school of mining and practical geology of Harvard university, Cambridge, Mass.; the Stevens institute of technology, Hoboken, N. J.; the school of mining and metallurgy of Lehigh university, Bethlehem, Pa.; the scientific department of the university of Pennsylvania, Philadelphia; the school of mines at Rolla, Mo.; the polytechnic department of Washington university, St. Louis, Mo.; the school of mines at Golden City, Colorado; and the university of California, Berkeley, Cal.