Ages before the dawn of civilization, primitive man had learned to extract certain ores and metals from the earth by subterranean mining. Such nations as the Egyptians, for example, understood mining in most of its phases, and worked their mines in practically the same manner as all succeeding nations before the time of the introduction of the steam engine. The early Britons were good miners and the products of their mines were carried to the Orient by the Phoenicians many centuries before the Christian era. The Romans were, of course, great miners, and remains of the Roman mines are still in existence, particularly good examples being found in Spain.

Even the aborigines of North America possessed some knowledge of mining, as attested by the ancient copper mines in the Lake Superior region, although by the time of the discovery of America, and probably many centuries before, the interloping races of Indians who had driven out or exterminated the Lake Superior copper mines had forgotten the art of mining, if indeed they had ever learned it. But the fact that their predecessors had worked the copper mines is shown by the number of stone mining implements found in the ancient excavations about Lake Superior, these implements being found literally by cart loads in some places.

The great progress in mining methods, however, as in the case of most other mechanical arts, began with the introduction of steam as a means of utilizing energy; and another revolution is in rapid progress owing to the perfection of electrical apparatus for furnishing power, heat, and light. Methods of mining a hundred years ago were undoubtedly somewhat in advance of the methods used by the ancients; but the gap was not a wide one, and the progress made by decades after the introduction of steam has been infinitely greater than the progress made by centuries previous to that time.

This progress, of course, applies to all kinds of mines and all phases of mining; but steam and electricity are not alone responsible for the great nineteenth-century progress. Geology, an unknown science a century ago, has played a most active and important part; and chemistry, whose birth as a science dates from the opening years of the nineteenth century, is responsible for many of the great advances.

Obviously a very important feature of any mine must be its location, and the determination of this must always constitute the principal hazard in practical mining. Prospecting, or exploring for suitable mining sites, has been an important occupation for many years, and has in fact become a scientific one recently. Formerly mines were frequently stumbled upon by accident, but such accidental discoveries are becoming less and less frequent. The prospector now draws largely upon the knowledge of the scientist to aid him in his search. Geology, for example, assists him in determining the region in which his mines may be found, if it cannot actually point out the location for sinking his shaft; and at least a rough knowledge of botany and chemistry is an invaluable aid to him. It is obvious that it would be useless to prospect for coal in a region where no strata of rocks formed during the Carboniferous or coal-forming age are to be found within a workable distance below the surface of the earth. The prospector must, therefore, direct his efforts within "geological confines" if he would hope to be successful, and in this he is now greatly aided by the geological surveys which have been made of almost every region in the United States and Europe.

An example of what science has done in this direction was shown a few years ago in a western American town during one of the "oil booms" that excited so many communities at that time. In the neighborhood of this town evidences of oil had been found from time to time—some of them under peculiar and suspicious circumstances, to be sure—and the members of the community were in an intense state of excitement over the possibility of oil being found on their lands. Prices of land jumped to fabulous figures, and the few land-owners that could be induced to part with their farms became opulent by the transactions. An "oil expert" appeared upon the scene about this time—just "happening to drop in"—who declared, after an examination, that the entire region abounded in oil. He backed up his assertion by offering to stake his experience against the capital of a company which was formed at his suggestion. Before any wells were actually started, however, a prudent member of the company consulted the State geologist on the subject, receiving the assurance that no oil would be found in the neighborhood. Strangely enough the word of the man of science triumphed over that of the "oil expert," and although some tentative borings were made on a minor scale, no great amount of money was sunk. It developed afterwards that the evidences of oil found from time to time had been the secret work of the "expert."

In general, prospecting for oil differs pretty radically from prospecting for most other minerals. A very common way of locating an ore-mine is by the nature of the out-crop,—that is, the broken edges of strata of rocks protruding from hillsides, or tilted at an angle on level areas. If the ore-bearing vein is harder than the surrounding strata it will be found as a jutting edge, protruding beyond the surface of the other layers of rocks which, being softer, are more easily worn away. On the other hand, if this stratum is soft or decomposable it will show as a depression, or "sag" as it is called. Of course such protrusions and depressions may only be seen and examined where the rocks themselves are exposed; vegetation, drift, and snow preventing such observations. But the vegetation may in itself serve as a guide to the experienced prospector in determining the location of a mine, peculiar mineral conditions being conducive to the growth of certain forms of vegetation, or to the arrangement of such growth. Alterations in the color of the rocks on a hillside are also important guides, as such discolorations frequently indicate that oxidizable minerals are located above.

In hilly or mountainous regions, where the underlying rocks are covered with earth, portions of these surfaces are sometimes uncovered by the method known as "booming." In using this method the prospector selects a convenient depression near the top of a hill and builds a temporary dam across the point corresponding to the lowest outlet. When snow and rain have turned the basin so formed into a lake, the dam is burst and the water rushing down the hillside cuts away the overlying dirt, exposing the rocks beneath. This method is effective and inexpensive.

The beds of streams, particularly those in hilly and mountainous regions, are fertile fields for prospecting, particularly for precious metals. Stones and pebbles found in the bed are likely to reveal the ore-foundations along the course of the stream, and the shape of these pebbles helps in determining the approximate location of such foundations. An ore-bearing pebble, well worn and rounded, has probably traveled some little distance from its original source, being rounded and worn in its passage down the stream. On the other hand, if it is still angular it has come a much shorter distance, and the prospector will be guided accordingly in his search for the ore-vein.

But prospecting is not limited to these simple surface methods. In enterprises undertaken on a large scale, borings are frequently made in regions where there are perhaps no specific surface indications. In such regions a shaft may be sunk or a tunnel may be dug, and the condition of the underlying strata thus definitely determined. This last is, of course, a most expensive method, the simpler and more usual way being that of making borings to certain depths. The difficulty with such borings is that rich veins may be passed by the borer without detection; or, on the other hand, a small vein happening to lie in the same plane as the drill may give a wrong impression as to the extent of the vein.

One of the most satisfactory ways of making borings is by means of the diamond drill. This drill is made in the form of a long metal tube, the lower edge of which is made into a cutting implement by black diamonds fixed in the edge of the metal. By rotating this tube a ring is cut through the layers of rock, the solid cylinder or core of rock remaining in the hollow centre of the drill. This can be removed from time to time, the nature and thickness of the geological formation through which the drill is passing being thus definitely determined.

CONDITIONS TO BE CONSIDERED IN MINING

Three great problems always confront the mine operator—light, power, and ventilation. Of these ventilation is the most important from the workman's standpoint, although the problem of light is scarcely less so. Obviously a cavity of the earth where hundreds of men are constantly consuming the atmosphere and vitiating it, and where thousands of lights are burning, would become like the black hole of Calcutta in a few minutes if some means were not adopted to relieve this condition. But besides this vitiation of the atmosphere caused by the respiration of the men and the burning of lamps there are likely to be accumulations of poisonous gases in mines, that are even more dangerous. Of the two classes of dangerous gases—those that asphyxiate and those that explode or burn—it may be said in a general way that the suffocating or poisonous gases, such as carbonic acid, which is known as black damp, or choke damp, are more likely to occur in ore mines, while the explosive gases are found more frequently in coal mines.

Choke damp, which is a gas considerably heavier than the atmosphere, is usually found near the bottom of mines, running along declines and falling into holes in much the same manner as a liquid. It kills by suffocation, and, as it will not support combustion, it may be detected by lowering a lighted candle into a suspected cavity, the light being extinguished at once if the gas is present. To rid the cavity of it, forced ventilation is used where possible, the gas being scattered by draughts of fresh air. If this is impracticable, and the cavity small, the choke damp may be dipped out with buckets.

But the problem of the mining engineer is not so much to rid cavities of gas as to prevent its accumulation. In modern mining, with proper ventilation and drainage, there is comparatively little danger of extensive accumulation of this gas.

The danger from this choke damp, therefore, is one that concerns the individual workman rather than large bodies of men or the structure of the mine itself. With fire damp, however, the case is different, as an explosion of this gas may destroy the mine itself and all the workmen in it. It is, therefore, the most dreaded factor in mining, and is the one to which more attention has been directed than to almost any other problem.

This fire damp is a mixture of carbonic oxide and marsh gas which, being lighter than air, tends to rise to the upper part of the mines. For this reason explosions are more likely to occur near the openings of the mine, frequently entombing the workmen in a remote part of the mine even when not actually killing them by the explosion. As this gas is poisonous as well as explosive the miners who survive the explosion may succumb eventually to suffocation.

Previous to the year 1816 no means had been devised for averting the explosions of fire damp except the uncertain one of watching the flame of the candle with which the miner was working. On coming in contact with air mildly contaminated with fire damp the candle flame takes on a blue tint and assumes a peculiarly elongated shape which may be instantly detected by a watchful workman. But miners were, and still are, a proverbially careless class of men even where a matter of life and death is concerned, and too frequently gave no heed to the warning flame. But in 1816 Sir Humphrey Davy invented his safety lamp, a device that has been the means of saving thousands of lives, and which has not as yet been entirely supplanted by any modern invention.

In making his numerous experiments, Davy had observed that iron-wire gauze is such a good conductor of heat that a flame enclosed in such gauze could not pass readily through meshes to ignite a gas on the outside. He found by experiment that a considerable quantity of explosive gas might be brought into contact with the gauze surrounding a flame, and no explosion occur. At the same time this gas would give warning of its presence by changing the color of the flame. When a lamp was made with a surrounding gauze having seven hundred and eighty meshes to the square inch, it was found to give sufficient light and at the same time to be practically non-explosive in the presence of ordinary quantities of gas.

One would suppose that such a life-saving invention would have been eagerly adopted by the men whose lives it protected; but, as a matter of fact, owing to certain inconveniences of Davy's lamps, many miners refused to use them until forced to do so by the mine-owners. One of these disadvantages was that this safety lamp gave a poor light overhead. This is particularly annoying to the miner, who wishes always to watch the condition of the ceiling under which he is working. When not under constant observation, therefore, a miner would frequently remove the gauze of the lamp and work by the open flame, regardless of consequences. Or again, he would sometimes forgetfully use the flame for lighting his pipe. To overcome the possibility of such forgetfulness or wilful disobedience, it was found necessary to equip safety lamps with locking devices, so that the miner had no means of access to the open flame of his lamp once it had been lighted.

Since the time of the first Davy safety lamp there have been numerous improvements in mechanical details, although the general principle remains unchanged. One of these improvements is a device whereby the lamp, when accidentally extinguished, may be relighted without opening it, and without the use of matches. This is done by means of little strips of paper containing patches of a fulminating substance which is ignited by friction, working on the same principle as the paper percussion caps used on toy pistols.

But even the improved safety lamp seems likely to disappear from mines within the next few years, now that electricity has come into such general use. As yet, however, no satisfactory portable electric lamp or lantern has been perfected, such lamps being as a rule too heavy, expensive, and unreliable. Even if these defects were remedied, the advantage would still lie with the Davy lamp, since the electric lamp, being enclosed, cannot be used for the detection of fire damp. But this advantage of the safety lamp is becoming less important, since well-regulated mines are now more thoroughly ventilated, and the danger from fire damp correspondingly lessened.

In some Continental mines the experiment has been tried of constantly consuming the fire damp, before it has had time to accumulate in explosive quantities, by means of numerous open lights kept constantly burning. This method is effective, but since the numerous lights consume the precious oxygen of the air as well as the damp, the method has never become popular. Obviously, then, the question of mine ventilation is closely associated with that of lighting.

Probably the simplest method of properly ventilating a mine is that of having two openings at the surface, one on a much higher level than the other if the mine is on a hillside, the lower one corresponding to the lowest portion of the mine where possible. By such an arrangement natural currents will be established, and may be controlled and distributed through the mine by doors or permanent partitions, or aided by fans. But of course only a comparatively small number of mines are so situated that this system can be used.

It is possible, of course, to ventilate a mine from a single shaft or opening by use of double sets of pipes, one for admitting air and the other for expelling it; but this system is obviously not an ideal one, and is prohibited by law in most mining districts. Such laws usually stipulate that there must be at least two openings situated at some distance from each other.

The older method of creating air currents was by means of furnaces, but this method, while very effective, is expensive and dangerous. In using this system a furnace is built near the outlet of the air shaft, the combustion of the fuel creating the necessary draught. But in the nature of things this furnace is a constant menace to the mine, besides being an extremely wasteful expenditure of energy. The modern method of ventilating is by means of rotary fans, the electric fan having practically solved the problem. The air currents established by such fans are controlled either by the doors in the passages, or by means of auxiliary fans. In addition, jets of compressed air are sometimes used, and have become very popular.

Another important problem that constantly confronts the mining engineer is that of drainage. Mines are, of course, great reservoirs for the accumulation of water, which must be drained or pumped out continually; and as the shafts are sunk deeper and deeper it becomes increasingly difficult to raise the water to the surface. Special means and machinery are employed for this purpose which will be considered more in detail in a moment.

ELECTRIC MACHINERY IN MINING

Electricity is, of course, the great revolutionary factor in modern mining. There is scarcely a department of mining in which electric power has not wrought revolutionary changes in recent years; and the subject has become so important and so thoroughly specialized as to "create a literature and a technology of its own." From the electric drill, working hundreds of feet below the surface of the earth, to the delicate testing-instruments in the laboratory of the assaying offices, the effect of this electrical revolution is being felt progressively more and more every year.

Moreover, electricity, on account of its transmutability, has made accessible many important mining sites hitherto unworkable. Rich mines are now in operation on an economical basis which, thirty years ago, were worthless on account of their isolation. When such mines were situated in mountainous regions where there was no coal supply at hand for creating steam power, and where the only available water power was perhaps several miles away, operations on a paying basis were out of the question before the era of electric power.

At present, however, the question of distance of the seat of power has been practically eliminated by the possibilities of electric conduction. A stream, situated miles away, when harnessed to a turbine and electric motors may afford a source of power more economical than could be furnished a few years ago by a power plant supplied with fuel at the very door of the mine. We need not enter into the details of this transmission of power, however, since the subject has been discussed in a general way in another place. Our subject here is rather to deal with the application of electricity to certain mining implements of special importance.

One of the most useful acquisitions to the equipment of the modern miner is a portable mechanical drill, which makes it possible for him to dispense with the time-honored pick, hammer, and hand-drill. But it is only recently that inventors have been able to produce this implement. The great difficulty has lain in the fact that a reciprocating motion, which is essential for certain kinds of drilling, is not readily secured with electric power. The use of steam or compressed air for operating such reciprocating drills presents no mechanical difficulties, and the fact that power of this kind can be transmitted long distances by the use of flexible tubes made such drills popular for several years. But the cost of operating such drills is so much greater than that of the new electric drills that they are rapidly being replaced in mining work.

The first attempts to produce an electric drill with a reciprocating motion were so unsuccessful that inventors turned their attention to perfecting some rotary device. This proved more successful, and rotary drills, operating long augers and acting like ordinary wood-boring machines, are now used extensively for certain kinds of drilling. The more recent forms perform the same amount of work as the air drill, with a consumption of about one-tenth the power. Moreover, none of the energy is lost at high altitudes as in the case of air drills, and they are not affected by low temperatures which sometimes render the air drill inoperable. On the other hand, the air drill is a hardy implement, capable of withstanding very rough usage, whereas the electric drill is probably the more economical, as well as the more convenient drill of the two.

In certain kinds of mining, such as in the potash mines of Europe and the coal mines of America, these electric drills operating their long augers have been found particularly useful. The ordinary type of drill is so arranged that it can be operated at any angle, vertically or horizontally. The lighter forms are mounted on upright stands, with screws at the ends for fastening to the floor and roof, although the heavier types are sometimes mounted on trucks. The motor, which is not much larger or heavier than an ordinary fan motor, is fastened to the upright and is from four to six horse-power. This connects with a flexible wire which transmits the power from the generating station, frequently several miles away. The auger, which is about the largest part of the machine and entirely out of proportion to the little motor that drives it, is simply a long bar of steel, twisted spirally at the cutting-end like an ordinary wood auger.

From the workman's standpoint these rotary drills are infinitely superior to reciprocating or percussion drills, where the constant jarring of the machine, besides being extremely tiresome, sometimes produces the serious disease known as neuritis. Various means have been attempted to prevent this, such as by overcoming the jar in a measure by flexible levers which do not transmit the vibrations to the hands and arms; but such attempts are only partially successful, and a certain amount of jarring cannot be avoided. In the rotary electric drills there is none of this, the workmen simply controlling the drill and the motor with levers, and receiving at most only a slight jar from the vibrations of the auger.

TRACTION IN MINING

In recent years electric traction engines for use in mines have been rapidly replacing horse-and mule-power, and have become important economic factors in mining operations. The pioneer of this type of locomotive seems to have been one built by Mr. W. M. Schlessinger for one of the collieries of the Pennsylvania Railroad about 1882, and which has remained in active use ever since. The total weight of this locomotive was five tons and it was equipped with thirty-two horse-power electric motors. The current was supplied through a trolley pole which took the current from a T-shaped rail placed above and at one side of the track. The train hauled by this locomotive consisted of fifteen cars, carrying from two to three tons of coal each.

Following this first mining-locomotive a great number were quickly produced. In Pennsylvania alone something like four hundred are now in use, and in Illinois two million tons of coal were hauled in this manner in twelve mines in 1901. It was estimated at the beginning of the present century that some 3,000 electric locomotives specially built for mining were in use in the United States alone.

The earlier types of mining-locomotives were much higher and bulkier than those of more recent construction, the motors being mounted above the trucks and geared downward. Very soon, however, the "turtle-back" or "terrapin-back" type was developed, with the motors brought close to the ground, so that even quite a heavy locomotive might not be much higher than the diameter of its driving-wheels. When these queer-looking machines were boxed in so that even the wheels were covered, they lost all resemblance to locomotives or vehicles of any kind, appearing like low, rectangular metal boxes placed upon the car tracks, that glided along the rails in some mysterious manner. The presence of the trolley pole helped to dispel this illusion, but in some instances this is wanting, the power being taken from a third rail.

With these locomotives, some of them not more than two and a half feet high, it was possible to haul trains even in very low and narrow passages—much lower, in fact, than could be entered by the little mules used in former years. This in itself was revolutionary in its effects, as many thin veins were thus made workable.

This type of low locomotive is the one that has come into general use throughout the world. Such locomotives range in size from two to twenty tons, with wheel gauges from a foot and a half wide to the standard railway gauge of four feet, eight and a half inches. Locomotives weighing more than twenty tons are not in general use on account of the small size of the mine entrances.

In the ordinary types the motorman sits in front, controlling the locomotive with levers and mechanical brakes placed within easy reach, but sunk as low as possible. As a rule, the motors are geared to the truck axles, either inside or outside the locomotive frame. An overhead copper wire supplies the current by contact with a grooved trolley wheel mounted on the end of the regulation trolley pole. An electric headlight is used, and the ordinary speed attained by the compact motors is from six to ten miles an hour.

The amount of work that can be performed by one of these little, flat, box-like locomotives is entirely out of proportion to its size. A 10-ton locomotive in a Pennsylvania mine hauled about 150,000 tons of coal in a year at a cost of less than one-tenth of a cent per ton for repairs. The usual train was made up of thirty-five cars, each loaded with about 3,700 pounds of coal, which was hauled up a three-per-cent grade. The cost of such haulage was only about 2.76 cents per ton, as against 7.15 cents when hauled by mule-power. These figures may be considered representative, as other mines show similar results.

THE LOCOMOTIVE "PUFFING BILLY" AND A MODERN COLLIERY TROLLEY.