MINING, the art of working mines, or of extracting minerals and mineral ores from the bowels of the earth.

This includes the scientific knowledge necessary for opening and working mines, and preparing the ores for use; it requires an intimate acquaintance with mineralogy and geology, as well as the different processes by which mines may be wrought to advantage, useful minerals searched out and brought to the surface, and means employed for mechanically and chemically separating metals from their ores; besides the essential operations of sinking shafts, driving galleries and adit levels, removing all difficulties which occur in the course of the work, propping up the superincumbent earth or rock so as to give security, to the miners, and constructing the machinery necessary either for draining mines or performing the requisite operations in the preparation and reduction of ores. The preparation of ores consists in breaking asunder the larger pieces, and then purifying them by means of water from the earth which adheres to them; in the separation of the coarser substances from the finer, by means of a sieve moved up and down in water; in the crushing of the ore in stamping-mills, by means either of hammers or iron cylinders; and, lastly, in the separation of the metallic substances from the stone or earth with which they are combined, by washing the crushed ore in troughs or on inclined tables crossed by a current of water, so that the heavier ore may remain, whilst the lighter substances are carried away by the stream of waler. Mining further includes the final purification of the ore by amalgamation or otherwise, and its reductions by means of· fusion. In the case where the object of mining is to obtain a mineral substance, as coal, which is fit for immediate use when brought to the surface, that term is employed in a more restricted sense, being limited to the operations which are requisite for the simple extraction and bringing up from the pit or mine the mineral in question.

I. The application of science to the art of practical mining has hitherto been made only to a limited extent. Yet the theory of the formation of mineral and metallic substances, and the rules which may lead to their discovery, are objects of much greater national importance than is commonly supposed. The circumstance^ under which minerals are usually found, the mode of obtaining them, and [7:15:276]their probable extent and value, are inquiries which, whilst they must ever be highly interesting to the man of science, who seeks knowledge for its own sake, are altogether essential to the mining proprietor, as affording the only means by which he can form a correct judgment respecting the mode of working adopted by the practical miner.

The advantage to be derived from a knowledge of well-established facts respecting the arrangement and distribution of mineral substances, will be best illustrated by examples of the errors and oversights committed where this knowledge was wanting. It is generally known that, for some years, lime was exported to New South Wales, where it exists in abundance in its natural state. In Cornwall, ores of silver and cobalt were, until recently, thrown away from a mine which has, since the discovery of their value, returned upwards of L. 10,000 a year from these ores; and in the same country, although celebrated for its tin mines from the earliest periods of history, yet, until last century, the ores of copper were employed only to repair the roads. Wherever the copper appeared in a lode, it was a common expression that the ore came in and “spoiled the vein and, even in the present day, but little attention is paid to whatever is not manifestly either tin or copper, or known to yield these metals. In Derbyshire, although lead has been smelted from the common blue ore ever since the time of the Romans, the other ores of the same metal were never thought of, but left in heaps, as rubbish; yet we have lived to see a public road, made and repaired with these rejected ores, actually taken up and smelted to good account. Instances might also be mentioned of persons who, in the belief that their estates contained valuable mineral veins, engaged in expensive workings, and sometimes ruined their fortunes; when a slight acquaintance with geology would have served to convince them that a successful result, if not impossible, was at least highly improbable. As to the practical miner, he is altogether the creature of habit, holding geology in but little estimation, and smiling at the nice distinctions of the mineralogist. Hence, if any inquiry be made of him respecting the interesting phenomena of veins, he generally prefers the theory of his forefathers to that which has been deduced from the results of more recent and accurate investigations.

In this country no public means have been employed for removing ignorance and counteracting prejudice in regard to the working of mines. But the case is different on the continent. Both France and Germany possess national institutions for facilitating the study of the sciences applicable to mining operations; and the advantage of such a course of education is sufficiently demonstrated by the fact, that the companies formed for working mines in South America and Brazil have given a decided preference to mining officers trained in the schools of France and of Germany. Besides, of all speculative employments, mining is perhaps the most uncertain. Experience and ingenuity are frequently baffled; the most promising appearances often end in disappointment; whilst from veins which some persons have abandoned in despair, others have frequently derived enormous profits. This very uncertainty, however, only affords another argument for concentrating all the lights of science, in order as far as possible to lessen the risk of disappointment, and to afford the miner some surer guide than chance or caprice in pursuing his exploratory labours.

It may be observed generally, that the materials which compose the crust, if not the body, of the earth, are variously distributed, yet preserve their relative positions, from the surface downwards to the greatest depths hitherto obtained; those substances which consist of homogeneous matter being collected together and deposited either above or below a similar stratum of other substances in a continued series of depositions. That these deposits were originally parallel with the earth’s surface may be reasonably supposed, and indeed appears to admit of almost no doubt; yet by some great convulsion of nature, some prodigious force acting upwards, the strata have been raised and broken through, whilst the corresponding parts being raised and depressed in different directions, the edges of the whole series have been elevated to the surface in an uniform curve or right line, appearing in the side of a cliff or mountain, or protruding in enormous masses of great extent and altitude; at the same time that the lower stratum still preserves the same relative position which it assumed in its original formation. By attending to this important fact, geologists are enabled to ascertain the order of stratification in any country or district, and thence to form a tolerably correct opinion respecting its mineral contents to a much greater depth than can ever be reached by mining operations.

If, for instance, the stratum be found to dip at a certain angle, by observing carefully the superincumbent strata, we may at once discover not only the depth at which a shaft proposed to be sunk will cut the stratum sought, but also the nature of the strata to be passed through in its course. The superincumbent strata will sometimes be found to vary in thickness, and a proportional allowance must then be made in the working for this deviation from the previous estimate. When the strata descend in the line of their dip or inclination, the depth to which they reach beneath the surface is unknown; but they are seldom found to continue their descent very far at the same angle, and are either curved in the coal formation, bent in another direction, or altogether dislocated. In the upper series or formation, the strata are not uniform in their construction, but are intersected by fissures resembling the bottom of a muddy pool dried up by the sun; and these cavities, when empty, are sometimes of great extent. Eldon Hole, and the other subterranean wonders of the Peak in Derbyshire, may be cited as remarkable examples of such dislocations. These fissures, however, are commonly filled with mineral substances, or metalliferous ores, in which case they are termed veins ; their inclination generally ranges from 45° to the vertical, or 90°; and their course downwards, like that of the strata, is seldom terminated within the limits of human labour and research. But some cases have nevertheless occurred where the metallic produce has to all appearance been worked out, or where the vein has branched into filamentous portions at two or three hundred feet below the surface.

Formerly the richest part of a vein of copper ore was supposed to be situated at a depth of from forty to fifty fathoms, and that of a vein of tin at from twenty to sixty fathoms; but experience derived from the deep workings carried on in Cornwall has proved this idea to be erroneous. When a vein or stratum is terminated abruptly, by the crossing of another vein or stratum in a transverse direction, or by perpendicular fissures filled with alluvial matter, this is not considered as a termination of the vein, which, in fact, is only broken off or disjoined, and may again be discovered by searching in the analogous part on the opposite side of the deranged strata. As to the methods employed in following a metalliferous vein when broken off by faults or dykes, these are necessarily various, according to circumstances; and it is in such cases that the practical knowledge and experience of the miner are of far more avail than all the suggestions of theory. Veins occur in almost every species of rock, and vary in thickness from a mere filament to many fathoms; they are very unequal in the different parts of their course, but they are commonly widest above. Narrow veins are usually short, whilst those of considerable breadth extend to a great distance. The silver vein of Veta Madre, at Guanaxuato, has been work [7:15:277]ed to the extent of 14,000 yards, at a depth of more than 570 yards, and from forty-three to fifty yards in thickness; and some other veins in South America have been traced to a distance of not less than eighty miles. A vein consists sometimes of one substance, at other times of many. In the latter case, these substances preserve an uniformity of position, parallel to the sides of the vein, in regular corresponding order, to the centre; so that, when traced downwards, the central seam first disappears, and the layers that enclosed it, being of homogeneous matter, coalesce, forming another central seam, which disappears in its turn, and is succeeded by the next, until a simple vein alone remains, gradually decreasing to its final termination. It has been observed, that veins similar to each other in mineral produce run parallel, or follow very nearly the same course throughout the district in which they are found, although occurring in different strata; and that veins containing other minerals in their immediate neighbourhood, or in the same stratum, always run in another direction. Thus, in Cornwall, when a vein of tin or copper ore, bearing east and west, is crossed by another running north and south, the intersecting vein is sometimes lead or antimony, but never tin or copper.

The principal metalliferous veins in England take a direction from east to west. When two veins running nearly parallel meet and join, they produce a good body of ore at the point of junction. If the principal vein dip at a less angle than the secondary one, it is usually found to be enriched by the latter; but if it dip at a greater angle, it is impoverished in like proportion. Sometimes a vein is joined by another, which, after falling into its course, and continuing for some distance to run parallel to it, suddenly resumes its original state, and breaks off in a different direction. For the most part, tin and lead lie nearer the surface than copper. Where the latter is met with in large masses, the vein commonly falls off shortly afterwards; but when the lode is found spotted with small portions of copper ore, there is a strong presumption that the produce will be rich and lasting. A large and productive vein is usually accompanied by others which fall into the main lode. The abundance of water in a lode is considered as a promising indication, inasmuch as dry veins are never very rich in ore. Lodes consist of hard solid stone, or less compact, soft, and crumbling materials. If the adjoining strata contain much spar and quartz, then the metalliferous ore in the lode is found in a solid, hard, stony substance; but when nature has been more sparing of her cement, the ore is generally met with in a loose and rub-bly state.

Experience has shown that certain minerals and metals are more frequently found attached to particular rocks than to other materials, and that some of them are discovered only in particular strata. Metalliferous veins are generally encompassed with some stone or other substance peculiar to the mine, which, from the appearance of the rock, apprises the miner of his approach to the vein. It has been ascertained that the arrangement of the materials of the earth is to a certain extent regular and uniform. Hence, when we know the particular substances near which certain metals and minerals are generally found, together with their usual disposition in the strata; and when, in another situation, we meet with the same materials similarly disposed; we may conclude with tolerable confidence, that the metal or mineral we are in quest of is not far distant, and that the operations may be continued with a reasonable prospect of success. Where a bed of mineral produce exists, it may be expected to extend throughout a considerable tract of country; but, from the curvature of formation, or from dislocation of the strata, it may nevertheless disappear at a particular point, and be lost, until it again rises to the “outcrop,” or is accidentally met with in boring or sinking a shaft at a considerable distance from the original working.

For the more complete elucidation of what has been stated above, we shall now describe shortly the several formations, with their general characteristics, the minerals which are usually found in them, and the localities in which the most important mines are situated.

The rocky masses composing the crust of the globe consist either of simple homogeneous bodies, as limestone; or of an aggregation of two or more simple materials, as granite. In some strata no organic remains whatever have been discovered; in others the fossil remains of animal and vegetable matter are of frequent occurrence. This diversity of character is the foundation of an arrangement, according to which rocks are divided into primary and secondary. The rocks belonging to the primitive formation are found under every other stratified mass, and never resting upon nor covering any; they follow a certain invariable order of succession, and exhibit determinate relations with other strata. Thus, granite is never found alternating with sandstone, nor gneiss covering a bed of coal. In mountainous countries, the primitive formation, upheaved in Alpine chains, offers itself to our notice in stupendous masses, having the strata of other formations resting upon and supported by their bases; or, as sometimes happens, without such formations altogether. Primitive rocks contain, either occasionally or exclusively, almost every metal hitherto discovered. They may be classed, in the usual order of their occurrence, under the denominations of granite, gneiss, mica slate, topaz rock, clay slate, porphyry, trap, limestone, serpentine, quartz, gypsum, flint slate, and syenite. Their component minerals are quartz, hornblende, felspar, mica, and limestone.

Granite is supposed to be the most ancient and most abundant of all substances. It forms the base and sometimes the whole mass of mountains; it constitutes a part of the Alps and the Pyrenees, the mountains of Cornwall, Saxony, and Silesia, the grand chain of the Ural and Altai in Asia, the Atlas in Africa, and the Andes and Cordilleras in South America. It is formed by a concretion of the granular particles of felspar, quartz, and mica, irregularly mingled, strongly adherent, and evidently the effect of simultaneous crystallization. The size, colour, and relative proportions of the particles differ greatly, but felspar with a reddish tint generally predominates. It is one of the hardest and most durable rocks known. Granite is much less metalliferous than any other of the primitive rocks; but it nevertheless yields tin and iron in considerable quantities, rarely gold or silver, and sometimes, in minute veins, molybdena, lead, copper, zinc, manganese, bismuth, galena, and blende.

Gneiss is immediately incumbent on granite, and is composed of the same substances; but mica, being more abundant, forms a granular slaty mass. This rock is rich in mineral produce; indeed all the useful metals, excepting quicksilver, are found in it, sometimes in beds, but more frequently in veins. The greater part of the mines in Saxony and Bohemia are in gneiss mountains. In the vicinity of Freyberg more than two hundred veins of silver, lead, tin, copper, and cobalt, have been worked in gneiss; and the silver mines of Königsberg are in the same rock. It is abundant in Scotland and the isles adjacent; and also in South America and the United States.

Mica slate, or schistus, is composed of mica and quartz. It has a slaty structure, mica being the chief ingredient; its colour is gray tinted with green or yellow, sometimes brown; and it differs from gneiss, upon which it rests, by being disposed in leaves rather than in distinct scales. It contains beds of magnetic iron ore; iron, copper, and arsenical pyrites; red iron ore, lead glance, blende, gold, and cobalt; whilst in the veins are found similar ores to [7:15:278]those discovered in gneiss. The mines of Dalecarlia and Fahlun in Sweden, the gold mines of Monte Rose, some of those in Saltzburg, the silver mines of Johann-Georgenstadt and Bransdorf, and many others, are in this rock. It is also common in Scotland, on the continent, and in many other parts of the globe.

Topaz rock is of very inconsiderable extent, and is hardly to be considered as a distinct species. It is composed of quartz, tourmaline, topaz, and lithomarge, in granular concretions; but it has hitherto been met with only in Saxony, where it forms a rock which is known by the name of schneckeìistein.

Clay slate is a simple rock, sometimes forming entire mountains; but the cliffs are not so steep and rugged as in granite and gneiss formations; and it is also much more favourable to vegetation. One of the varieties of this stratum is the well-known material for covering roofs of buildings; the rest partake of its general characters. It passes by different gradations into mica slate, acquiring a glistening lustre in its approach to that formation; it is distinctly stratified, and is rich in metal, containing tin, lead, cobalt, silver, pyrites, copper ore, and sometimes gold. The veins in Cornwall often run in killas, which is a variety of clay slate; and some curious phenomena occur in their passage through the strata. If the vein contain tin ore in the granite, it will frequently change to copper in the killas; and if tin be abundant in the killas, copper will supply its place in the granite. This rock is very widely distributed, and occurs in all parts of the world. In Saxony, Bohemia, Hungary, and in North and South America, mines are worked in it, some er them to a very considerable extent.

Porphyry consists of crystals of quartz or felspar in a cement of hornstone or claystone; it is not stratified, nor do any mineral beds occur in it; and its colour varies according to the nature of the basis, although red and black are the most common. It is so hard that the art of cutting it for sculpture is now lost; indeed modern tools make no impression on the surface, although huge columns, and many beautiful specimens of chiselling, remain to convince us that it was practised by the ancients in great perfection. Many metalliferous minerals are found in porphyry. The mines of Hungary are worked in enormous rents or fissures in this rock. Porphyry also appears in Cornwall, Sweden, France, Saxony, Carinthia, Hungary, Siberia, Abyssinia, and North and South America.^[1. See Mining Review, No. V. p.. 13, et seq. ]

For details as to the mineral deposits contained in the other primitive rocks, the reader is referred to the article Mines, where, under the different heads, ample information will be found on this, as well as on various other matters connected with the present subject.

II. One of the most important operations of practical mining is that of blasting, of which we shall now proceed to give some account.

The first part of the process consists in preparing or boring the hole for the reception of gunpowder. This is effected with the sharpened bar and the borer, represented in fig. 1, the length and breadth of both being variable. The shaded portion a, which is the cutting part, is of tempered steel; and the upper part, which is held by the workman, consists of iron. In the western part of Cornwall, the borer is held in one hand and the hammer in. the other, the operation being performed by one person; but in the central and eastern parts, one person usually holds the borer, whilst another applies the hammer or mallet. From the borer being kept constantly in motion, the hole is made of a circular form, its depth varying from eight inches to five feet, and its breadth from one to three inches. Water is poured into the hole if none issue from the rock, to facilitate the operation of the borer; and the abraded matter is withdrawn by the scraper, fig. 2. It is afterwards further cleaned with a piece of wood, called a swab-stick, one end of which is prepared for the purpose. When the hole is inclined, and intended to be deep, a long borer is used, which one man raises and lets fall, the operation being for the most part performed by the momentum acquired by the instrument in descending from the height to which it is raised. This is called “jumping If the hole be dry and much inclined, the gunpowder is now poured into it, the quantity requisite being at first guessed; but after a few explosions, it is seen whether the proportion employed be a just one or not, that is, sufficient to fracture the rock without breaking it in pieces and scattering them to a distance. If the latter effect be produced, the quantity of powder is diminished; but if the rock be not fractured, it must be increased. As some of the gunpowder will adhere to the moist sides of the hole, this must be wiped down with the and of the swab-stick. If the rush be used to convey a spark to the charge, a piece of clay is laid upon it, and through both the needle is inserted until it reaches nearly to the bottom of the hole.

The nail, fig. 3, is a metallic rod gradually tapering to a point, and at the other end it is formed into a ring. It was formerly made entirely of iron; but latterly its pointed extremity has been made of copper, because, during its insertion or removal, the iron-pointed nail Sometimes caused ignition, and thus led to fatal consequences. Next to the powder is put some dry substance, and then clay, upon which are put down and gently beaten with the tamping or ramming bar, fig. 4, pieces of some stony substance, which readily yields to the hammer without giving a spark, as roofing tile, soft slate, decomposing porphyry, friable granite, coal, or solid copper, which are all occasionally used. At first a little is put in and beaten firmly down; then a second small quantity, a third, a fourth, and so on until the hole be entirely filled. It is desirable that each layer should be very thin, as the confining power of the tamping is considered to be in proportion to the number of layers; but this must be understood within certain limits. The tamping bar is usually made of iron, the lower extremity being shod with copper or brass; Dr Paris found, however, that an alloy of eighty-six parts of copper and fourteen of tin proved the most durable. The next point is the removal of the nail, which is effected by striking it upwards, or by the use of a lever. The rush is then introduced into the hole left by the nail, the pith having been first removed and its place filled with fine gunpowder. When all this has been done, nothing remains but the application of the fire, which is communicated by the ignition of one end of a match, or a piece of coarse paper smeared with grease, the other end being placed in contact with the [7:15:279] rush, and the slow combustion affording time for the escape of the workmen.

The ignition of the charge, however, is frequently effected by the train being contained in a rod of quills, or by the use of Bickford’s patent safety-rods. When either of these is employed, it is placed in the hole before the introduction of the charge; and in these cases the nail is not required. The operation of tamping is in every respect conducted as before. The rod of quills is merely a tube of common goose-quills, the smaller end of one being inserted in the larger extremity of another, until the tube be of the length required, that is, equal to the hole bored in the rock. The gunpowder with which the tubes are filled should be bruised to dust, and packed very closely in the tube. It might be thought that the compression to which such tubes are exposed during the process of tamping would prevent their combustion; but this is not the case, for so strong are they, when properly filled, that even the pressure of a smith’s vice would produce no such result. The patent safety-rod is a column of gunpowder enveloped in a series of hempen yarns twisted spirally round it, and perfectly flexible. It is about three eighths or one half of an inch in diameter, consumes slowly, and rarely becomes extinguished until it be entirely burnt. The expense of the quills and the safety-rods is nearly the same, that is, threepence per fathom in length.

The preceding remarks are intended to apply to an inclined perforation. But when the aperture is nearly horizontal, which is frequently the case, the introduction of the charge is somewhat more difficult. Some miners make a cartridge or tube of paper, which they cement with grease, and which, being filled with fine gunpowder, is pushed with the swab-stick to the further extremity of the hole; others charge with the fluke, which may be described as the half of a hollow cylinder divided in the line of its axis, and being attached to the end of an iron rod, fig. 5, resembles a carpenter’s auger, or a marrow-spoon. The tamping is in all cases alike, and the train may be laid in either of the ways already mentioned.

But when the hole has been moistened by the infiltration of water, the operation is much more difficult, and is accomplished either by claying the hole, or by introducing the charge in a pitched bag or tin-plate cartridge. Claying consists in filling as much of the further extremity of the hole as the charge is intended to occupy, with stiff clay, impervious to water, or at least very nearly so. Through this clay a cylindrical bar, usually made of iron, is pushed nearly to the extremity of the perforation, in order to make a space for the reception of the charge, which is at once introduced, and then the hole is tamped and the train laid in the ordinary manner. This operation requires to be performed with great rapidity, because the clay not being quite impervious to water, may become saturated, and the charge moistened, so as not to ignite when the train is fired. The pitched bag, above mentioned, is made of canvass, and so covered with pitch as to be impenetrable to water; the tin-plate cartridge is simply a tin case in a cylindrical form. When the bag or cartridge is used the charge is placed in it, the train for its ignition being laid through a tin-plate tube about one fourth of an inch in diameter. This receptacle is placed in the further extremity of the hole, sometimes imbedded in clay, and is tamped in the usual manner. The pitched bag is preferred to the cartridge, because the one fits the hole more exactly, whilst the regular figure of the other retains round it a little air, which, in yielding to the compressing force, impedes the full effect of the explosion.

An apparatus, invented by Captain Chenhalls, of St Just, in the western part of Cornwall, and denominated the shifting cartridge, has been found useful in charging holes of small depth. Fig. 6 represents a section of this instrument. It consists of a copper cylinder a b,∙ two feet in length, and one inch in diameter, containing a moveable rod c, which is graduated in inches, and has affixed to its extremity a leaden plug d, whilst the cap g is made to take off, in order to allow, at any time, the removal of the rod, for cleaning the interior. The manner of using it has been thus described. Draw out the rod as many inches as you require it to deliver of gunpowder, then invert the instrument, fill it, and place a piece of moistened clay at the mouth of the cylinder; it is now to be inserted in the hole, when, by pressing down the sliding-rod, the whole charge is immediately delivered in a mass without any loss; but before the instrument is withdrawn, the rod should be several times rammed down smartly upon the gunpowder. In charging back holes, that is, holes nearly horizontal, the clay should be stuck upon the end of the plug d previously to the introduction of the powder into the cylinder. When quills are used for a fuze, it will be found advantageous to affix in the cylinder a smaller tube for their reception, as represented by er. Much has been said as to the waste of gunpowder in mines in consequence of the ignorance or carelessness of the workmen; and there is probably some ground for censure in this respect. But, on the other hand, whilst it is difficult for any but a practical miner to say where a perforation can be advantageously made, so nothing but experiment can determine the quantity of gunpowder requisite for any given hole, and this must necessarily be left to the workmen.

It has been frequently asserted that sand is a good and efficient substitute for tamping, as commonly practised; and numerous experiments have been made to establish this point, but hitherto without any very satisfactory results. In many cases the sand has been blown out, whilst, in some instances, effective explosions have ensued. Further experiments are certainly required to set this important point at rest, by determining the circumstances upon which success or failure depend.

With respect to accidental or premature explosions, by far the larger portion of these either originate from the nail, or are produced in the course of the tamping process. Those which originate through the nail occur only when the rush is used, and although the number of accidents has been considerably diminished since it was pointed with copper, yet even this has not entirely prevented them. They are caused, first, by the nail being driven to the very bottom of the hole, and its there coming in contact with substances which by percussion generate a spark; secondly, the nail, during the tamping, is subject to concussion, which, in certain circumstances, will produce a similar effect; and, thirdly, the removal of the nail may occasion a like result, especially if, when introduced into the hole, it had been so forcibly driven to the bottom as to bend its point, for in this case the curved part will occasion considerable disturbance in the contents of the hole, and the danger will not be materially diminished by the circumstance of the nail being pointed with copper. But by putting a small piece of clay at the bottom of the hole, and by taking care not to force the nail against its lower extremity, the hazard arising from this cause may in a great measure be obviated. The dangers incident to the tamping process spring chiefly from the gunpowder adhering to the sides of the hole; so thaf, if a spark be struck out during the operation, it will communicate to these particles, and ignite the charge. Fire may be struck, first, by the contact of the tamping bar with such portions of the sides of the hole as are calculated to afford a spark from collision; secondly, by the action of this instrument upon portions of the tamping, when the bar is not shod with copper or brass; thirdly, by the friction of such substances in tamping, against similar bodies in the sides of the hole; and, fourthly, by the friction of various parts of the tamping[7:15:280] against one another. The precautions to be used against the occurrence of accidents of this kind are, first, removing carefully the adhering particles of gunpowder from the sides of the hole; secondly, the use of a tamping bar shod with a substance which does not readily strike fire; and, thirdly, care in selecting substances for tamping which do not readily afford sparks by impact upon one another. Notwithstanding the use of quills and safety-rods, explosions of this class sometimes occur, their causes being apparently beyond the reach of such contrivances. But of the fatal acbidents which have occasionally happened, the greater part are attributable to the carelessness of the workmen, rather than to their ignorance. Many explosions have originated from want of caution in boring a charge which has not ignited owing to the train having somehow been extinguished. In such cases, the tamping is removed by the borer, and, from the indifference of habit, the workmen frequently take no more care than if they were forming, or “beating down,” a new perforation.^[2. Mining Review, No. VI. p. 240, et seq. ]

III. Humboldt, speaking of the state of the mining art in Mexico strongly censures the method of blasting by powder, as therein employed. The holes for the reception of the cartridges are, he thinks, generally too deep, and the miners are not sufficiently careful in diminishing the mass of rock intended to yield to explosion. A great waste of gunpowder is consequently occasioned. In the mine of Valenciana, powder to the amount of L.150,000 was consumed from 1794 to 1802; and the mines of New Spain annually require from 12,000 to 14,000 hundredweights. Humboldt thinks it probable that two thirds of this quantity is uselessly employed.

The timber-work is also, according to him, very carelessly performed, although it ought the more to engage the attention of the proprietors of mines, as wood is every year becoming scarcer on the table-la<ιd of Mexico “The masonry employed in the shafts and levels,^[3. Especially in the mines of Valenciana, Guanaxuato, and Real del Monte. ] and especially the walling with lime, deserves great praise. The arches are formed with great care; and in this respect the mines of Guanaxuato may stand a comparison with whatever is most perfect at Freyberg and Schemnitz. The shafts, and still more the galleries or levels, have generally the defect of being dug of too great dimensions, and of occasioning, by that means, exorbitant expenses. We find levels at Valenciana,^[4. Canon de la Soledad. ] executed with the view of making trial on a poor vein, of a height of twenty-six or twenty-nine feet. It is an erroneous opinion, that this great height facilitates the renovation of the air; the ventilation depends on the equilibrium and difference of temperature between two neighbouring columns of air. They also believe, equally without foundation, that, in order to discover the nature of a powerful vein, very large drifts are requisite, as if, in mineral veins of from six to eight fathoms in width, it were not better to cut from time to time small cross drifts, for the purpose of discovering whether the mass of the vein begins to grow richer. The absurd custom of cutting every evel of such enormous dimensions prevents the proprietors from multiplying the means of trial, so indispensable for the preservation of a mine and the duration of the works. At Guanaxuato the breadth of the oblique shafts dug stairwise is from five to six fathoms; and the perpendicular shafts are generally three, four, or five fathoms in diameter. The enormous quantity of ores extracted from the mines, and the necessity of working in them the ropes attached to six or eight whims, necessarily occasion the shafts of Mexicoto be made of greater dimensions than those of Germany; but the attempt which has been made at Bolanos, to separate by beams the ropes of the whims, has sufficiently proved that the breadth of the shafts may be diminished without any danger of the ropes getting entangled in their oscillatory motion. It would in general be very useful to make use of kibbles instead of leathern bags suspended by ropes for the extraction of the ores.

“The greatest fault observable in the mines of Néw Spain, and which renders the working of them extremely expensive, is the want of communication between the different works. They resemble ill-constructed buildings, where, to pass from one adjoining room to another, we must go round the whole house. The mine of Valenciana is justly admired on account of its wealth, the magnificence of its walling, and the facility with which it is entered by spacious and commodious stairs; yet it exhibits only a union of small works irregularly conducted; they are as it were cul de sacs, and without any lateral communication. I mention this mine, not because it is more faulty than the others in the distribution of its labours, but because we might naturally suppose it to be better organized. As subterranean geometry had been entirely neglected in Mexicotill the establishment of the School of Mines, there is no plan in existence of the works already executed. Two works in that labyrinth of cross levels and interior winzes may happen to be very near each other without its being possible to perceive it. Hence the impossibility of introducing, in the actual state of most of the mines of Mexico the wheeling by means of barrows, and an economical disposition of the ore plats.”

The same distinguished traveller has also animadverted on the defective machinery employed in working and draining the Mexican mines. “We have already spoken of the truly barbarous custom of drawing off the water from the deepest mines, not by means of pump apparatus, but by means of bags attached to ropes which roll on the cage of a whim. The same bags are used in drawing up the water and the ores; they rub against the walls of the shafts, and it is very expensive to keep them in repair. At the Real del Monte, for example, these bags only last seven or eight days; and they commonly cost five, and sometimes seven and eight shillings a piece. A bag full of water, suspended to the cage of a whim with eight horses {malacate doble), weighs 1250 pounds; it is made of two hides sewed together. The bags used for the whims called simple, those with four horses (malacates sencillos'), are only half the size, and are made of one hide. In general the construction of the whims is extremely imperfect; the bad custom also prevails of forcing the horses, by which they are made to go at far too great a speed. I found this speed at the shafts of San Ramon, at Real del Monte, to be no less than ten feet and a half per second; at Guanaxuato, in the mine of Valenciana, from thirteen to fourteen feet; and everwhere else I found it more than eight feet. Don Salvado Sein, professor of natural philosophy at Mexico has proved, in a very excellent paper on the rotatory motion of machines, that, notwithstanding the extreme lightness of the Mexican horses, they produce only the maximum of effect on the whims when, exerting a force of 175 pounds, they walk at a pace of from five to six feet in the second.

“It is to be hoped that pumps, moved either by horseengines of a better construction, or by water-wheels, or by pressure-engines, will at last be introduced in the mines of New Spain. If wood, and coal, which has only yet been discovered in New Mexico should be found sufficiently abundant for employing the steam-engine, the use of it would be of great advantage in the inundated mines of Bolanos, as well as in those of Rayas and Mellado.

“It is in the draining the mines of water that we particularly[7:15:281] feel the indispensable necessity of having plans drawn up by subterranean surveyors (géomètres). Instead of stopping the course of the water, and bringing it by the shortest road to the shaft where the machines are placed, they frequently direct it to the bottom of the mine, to be afterwards drawn off at a great expense. In the district of mines of Guanaxuato, nearly two hundred and fifty workmen perished in the space of a few minutes, on the I4th of June 1780, because, not having measured the distance between the works of San Ramon and the old works of Santo Christo de Burgos, they had imprudently approached this last mine while carrying on a drift in that direction. The water, of which the works of Santo Christo were full, flowed with impetuosity through this new gallery of San Ramon into the mine of Valenciana. Many of the workmen perished from the sudden compression of the air, which, in taking vent, threw to great distances pieces of timber and large masses of rock. This accident would hot have happened if, in regulating the operations, they could have consulted a plan of the mines.” (a.)