and shut the stop-cocks alternately as it was required. | This was accomplished by catches (scoggans) worked by the beam, or strings connected with the lever of the valves and the beam-an invention of a boy, Humphrey Potter, to avoid the trouble that constant attendance on the levers demanded. By means of a plug frame fixed to the beam, invented by Beighton, the engine was made to work the valves with great regularity—a most important practical advance in making the stear-engine work itself, and adjust its own valves. The analogous part of this machinery in the modern double-acting engine is to be observed in the eccentric. This, the atmospheric or Newcomen's engine, had many and very striking advantages over all others previously proposed. It may, indeed, be considered the basis of the engine subsequently modelled by Watt. But there were very serious defects in it, which the reader will in some measure be acquainted with from the history of Watt's engine. It is here sufficient briefly to enumerate them. Much steam must, then, be lost during the process of the heating of the cylinder after each con densation; for it must always at least be raised to the temperature of the steam before the steam can, as such, continue in it, and be in any degree efficient; and on the other hand, the cold air which follows the descent of the piston must necessarily withdraw a considerable portion of heat. By the calculations of Watt, it was esti mated that three times as much steam was expended in this manner as would have been equal to work the engine -a loss, therefore, equal to 75 per cent. Nevertheless, this, as has been correctly observed, "was the first really efficient steam-engine; that is, the first engine which could be applied profitably and safely to the most important purposes for which such machines were required at the time of its invention." In the further history of steam-engines, we fall on the era of Watt, the atmospheric engine having been very extensively used for a period of nearly one hundred years. The modifications it afterwards underwent have been sufficiently explained in the history of Watt's engine, and it is therefore unnecessary to extend these observations further. MINING-METALS-COAL-SALT. THE objects upon which mining industry is exerted | are, as is well known, metals, coal, salt, and various kinds of earths and other substances employed as drugs, or in different departments of the useful arts. Confining our paper to the mining industry of the British islands, which are rich in mineral products, we shall, in the first place, treat of the metallic class of minerals, such as tin, copper, iron, lead, &c., and afterwards of coal and salt. METALLIFEROUS DEPOSITS. Metals are not distributed accidentally and promiscuously in the earth, nor do they exist, with rare exceptions, n a pure and unalloyed state. They are found in connection with various earthy impurities, and in different states of chemical combination with other mineral substances. Such deposits are called metalliferous, or containing metal. The chief forms in which they occur are veins, beds, and fragmentary deposits. Fragmentary deposits are associated with many of the superficial beds of sand and gravel which occur in the valleys of mineral districts, consisting of the detritus of the neighbouring metalliferous mountains, which has been washed down from them at remote geological epochs. These mineral accumulations are not equally and indiscriminately mixed up with the sands and alluvial matter, but the excess of their specific gravity has occasioned their separation into distinct layers, commonly found towards the bottom of the alluvium. It is well known that minute grains of gold, or gold dust, are interspersed in this manner with the sands of the Brazils; and it is estimated that the gold derived from the washings in the chief province of the Brazilian gold district produces about 2800 pounds of fine metalworth nearly one million of pounds sterling. It is less generally known that there exist three small gold washing stations in the county of Wicklow in Ireland. Little streams running from the mountains are slightly diverted mto reservoirs, where the particles they deposit undergo divers washings in wooden bowls, and among the purified remains are discovered rare grains of gold. On the occasion at which we visited these washing places, the produce of the morning's labours at one of them was about six shilling's worth of gold. Tin ore is also found in Cornwall, in deposits generally considered alluvial, mixed with the debris of differ ent rocks, and often covered with an alluvial bed. Repeated washings, by means of running water, being the chief process by which such ore is separated, the name of stream work is commonly applied to this method of obtaining it. The water being excluded from one of the branches of Falmouth harbour, a bed of rounded masses of tin ore, from two to ten feet thick, was found fifty feet below a bed of alluvium—£50,000 was made by this discovery. Beds. By mineral beds are meant the metalliferous strata which sometimes alternate with earthy strata. Mineral beds are for the most part horizontal, or slightly inclined, and occur in what are geologically termed primitive and secondary countries, of various elevations. The ores of copper, iron, and lead, occasionally occur together in beds in primitive mountains, and sometimes small quantities of gold and silver are mixed with them. Cobalt and certain ores of mercury also occur in beds. Almost all the ores of metals in the great mining dis trict of Sweden are found in beds in primitive mountains. Lead, zinc, and iron ores, occur abundantly in beds in secondary mountains. In England, the principal metal whose deposits assume the form of beds is iron, in the state called ironstone. This alternates in thin beds with beds of coal, and frequently with beds of limestone. Thus the metal, and the means of heating and fluxing it, are most fortunately combined in one and the same locality. One of the most important mineral productions of Scotland is the thin bed of ironstone called black-band, which is not known to exist beyond a space of from eight to ten square miles in the mineral district around Airdrie, near Glasgow. The true black-band is found from fifteen to sixteen fathoms below the splint coal, and is only from fourteen to eighteen inches in thickness. The "output" from Rochsolloch is 4500 tons per month; and the an per annum, on a property which, if let for tillage, would yield only a few hundreds a year. Some of the ironstone beds, as in south Staffordshire, consist of pulverized matter, with rounded boulders of ironstone distributed through it; and some few contain flattened spheroids, or roundish masses. The beds of ironstone being common.y situated at a much less depth, and being more readily arrived at than veins of metals in general, the pits are both shallow and simple, and therefore require no particular notice. In this country they are worked principally in south Staffordshire, Shropshire, south Wales, and the eastern and western mineral fields of Scotland. nual income to the proprietor amounts to about £12,600 | of from one to three feet in width are usually less intermixed with foreign and troublesome substances than those which are wider. A vein of tin in a mine called Whealan Coates was only three inches wide, and yet proved so rich as to be worth working. Some of the veins containing copper in Herland mine did not exceed six inches in width; and after continuing this thickness for a few fathoms, eventually passed away east and west in mere strings; but they yielded copper of a very rich character. In the next hill there was also a very productive copper vein of from twelve to twenty-four feet in width. The compositions of the lodes or veins are as variable as the nature of the rocks through which they pass. By far the greatest portion of them, however, is earthy matter, of the nature of the contiguous rock, but also containing large intermixtures of quartz. These ingredients occasionally occur in separate veins, but for the most part they are mingled without regularity or order, and throughout them are dispersed the metallic ores. times they are aggregated very thickly, and very generally occur in large irregular lumps or patches called bunches, connected with each other by small veins of ore. At other times the ore is very sparingly sprinkled through the whole of the earthy matter of the vein, and in some rare instances it forms the larger part of its contents. The sides of metalliferous veins are generally very determi nate, being covered by a hard, dark-coloured crust, called by the miner the walls of the vein. Veins are the principal forms in which metallic ores are distributed throughout the globe. A description of the veins of Cornwall will almost suffice for those of every other country, as the differences are of a comparatively unimportant character to the general observer. A vein may be said to resemble a deep cleft or crack in a clayey field, which has been subjected to the exhaling influences of the hot sun for some time. This cleft, whatever may be its depth, must of course have a direction under ground, either slanting or straight; and if we suppose it filled with metallic ore, we form the idea of a vein, or, as it is provincially termed in Cornwall, a lode; if we suppose the cleft filled with any other stony substance, we can imagine what is called a non-metalliferous vein, of which there are many, sometimes pursuing their own exclusive courses, and at others intersecting the metalliferous veins. The direction of the lodes is by no means accidental, but nearly determinate. They usually run east and west, and dip or underlie either towards the north or south; while the non-metalliferous veins, which run north and south, dip either towards the east or west. The cases in which metalliferous veins assume a north and south direction are few, and chiefly foreign. It frequently happens that the metalliferous lodes, as we have said, cross each other; and, as a leading fact, the intersection of two lodes at a small angle is productive of good ore. Should, however, a copper lode pass through a tin lode, the copper lode invariably divides the tin lode, and generally heaves it out of its course, to the frequent perplexity and loss of the miner. All mining experience of a general character is, however, sometimes set at defiance; for, in the small space of one little hill, instances may be found in which veins of almost every description dip or underlie in almost every possible direction, traversing each other in such a manner as completely to baffle the miners; but it is an ascertained fact, that there are seldom or never, in the same district, two series of metalliferous veins running at right angles to each other. As a tolerable average, we may assume the direction of the Cornish lodes to be about four degrees south of true west, and their dip or inclination to average sixty or seventy degrees from the horizon. Taken on the whole, the lodes appear tolerably straight both in direction and inclination, but when examined in detail, they exhibit almost continual curvatures and irregularities in both respects, although these flexures would seem to be projected on certain lines which manifest considerable con stancy. The length of no one lode has yet been satisfactorily traced. Some of them, indeed, have been followed for two or three, or even four or five miles; but no instance has occurred in which a vein has been known to stop; nor has the miner ever yet seen the bottom of one, although there are several mines in Cornwall upwards of 1000 feet in depth from the surface, and two or three about 1300 feet deep. The lodes differ exceedingly in respect of width, in which, indeed, they vary from a mere line to forty or fifty feet. On the average, they may be assumed to be three feet and a half wide. Lodes Some We have noticed that there is a second series of veins, called non-metalliferous veins, which run north and south; that is, nearly at right angles to the metalliferous lodes. When these veins are chiefly composed of quartz, they are locally denominated cross-courses, and when consisting mostly of clay, they are named "flucans." Their general direction, when accurately traced, is about south-east and north-west. Their dimensions are variable, being perhaps on an average about two feet; their dip, too, fluctuates, but, as a general rule, it is greater from the horizon than that of the lodes. The clay with which the flucans are filled invariably partakes of the same character as the contiguous rock. Tin and copper ores are occasionally found in small quantities in the cross-veins, and in two or three instances silver and its ores have occurred in them to some amount. The chief metallic produce, however, of this class of veins, is lead ore; but this they seldom yield in the neighbourhood of lodes which have been productive of other metals Indeed it is, as we have said above, a general law in Cornwall, that two series of productive metalliferous veins, at right angles to each other, are very seldom or never found in the same district. Both the lodes and the cross-veins ramify and divide; and whilst the part which in one place is large will sometimes, within a short distance, dwindle and die away, the portion which is small, where the other is rich, will often, within a small space, enlarge and become productive. As these two series of veins, the lodes and the crossveins, run at right angles to each other, they of course frequently meet and intersect. In a few instances the lodes traverse the cross-veins, but in far the greater number of cases the cross-veins cut through the lodes. O casionally, the cross-vein simply intersects the lode, but more generally displacements, provincially termed heares, attend their contact. These heaves, although usually only amounting to displacements of a few feet or fathoms (a fathom being equal to six feet), yet in some cases turn off 20, 30, or 40 fathoms, and in one instance to the extent of 72 fathoms. If, for example, a cross-vein, in its north or south course, meets with a lode containing copper or tin, the last seems to have been split, as it were, into numerous little branches by the first, which generally pursues its uninterrupted course straight for wards. Another effect, too, of a much more extraordinary kind, is produced by this intrusive cross-vein. In Situation of Metalliferous Deposits. searching for the tin or copper lode on the other side of beautiful groups of dazzling brilliance. It has been ele this north and south vein, a lengthened period frequently gantly though fancifully observed, that minerals are the elapses before the fugitive can be discovered. Notwith-flowers of rocks; and might we not, in pursuance of the standing the experience of the miners, forty years have same idea, call these cavities the gardens of the mineral sometimes passed over, before the search, though carried kingdom? It is from these open spaces that most of the on with vigour and great expense and labour, has proved mineral specimens are collected for the cabinets of the successful. It is by no means a simple task for the mining curious and the wealthy. engineer to lay down a law for the recovery of the lode. Instances have been known in which it has been again found 120 or even 450 feet north or south of its original course. The cross-vein will not perhaps generally intersect the lode exactly at right angles, but its inclination to the course of the lode will usually be such as to produce at the intersection an obtuse angle at one side of the lode, and an acute at the other side; and it is thought, by the most experienced observers, as well in Saxony as in Cornwall, that the second portion of the lode will more frequently be discovered on the side of the obtuse angle, formed by it with the cross course, than on the side of the acute angle. In other words, on whichever portion of the lode we approach the cross-vein, the other portion will be found towards the same hand, namely, the right hand. There are other kinds of interruption to which metalliferous veins are subject, though far less extensive in their agency than the cross-veins. These are denominated slides, and generally consist of clay or argillaceous matter. Their direction is nearly parallel to that of the contiguous lodes, but their dip or underlie being either greater than, or opposed to, that of the latter, they intersect them either in a horizontal or more or less inclined direction. Slides are common in Cornwall, and occur also in Mexico and other mining countries. It is a well known but remarkable fact, that some of the metallic ores lie much nearer to the surface than others. Gold, in the small veins of it which are sparingly distributed through some of the rocks in Brazil and elsewhere, is worked by open cuttings from the surface. Silver is found in some foreign mines at a depth of from two to three hundred feet, while the silver mines of Mexico are of a much more considerable depth. Tin is also found at shallow depths, of which the great lode of the Charleston mines in Cornwall furnish a good example. Lead is usually met with at a very trifling depth, and slightly spotted veins of it are sometimes to be observed in the sides of brooks, and in the rocky channels of rivers. Copper, on the contrary, generally lies deep, and the enormous deposits of this metal found in Cornwall are generally situated two or three hundred feet below the surface. Where tin and copper are found together in the same vein, the tin commonly occupies the upper part, and disappears at the depth at which the copper is discovered. Sometimes, however, the ores of both metals occupy the vein together to a great depth, as at the Poldice mine near Redruth. On referring to the known depths to which different metals extend, it will be found that those which commonly lie near the surface, as lead, zine, gold, and occasionally tin, do not generally penetrate to any great depth; while those which lie deeper, as copper and silver, are worked in the bottoms of our deepest mines. This coincidence may be the result of a natural law, or it may be apparent, and consequent only upon the limit of our experience and knowledge. Cavities or open spaces frequently occur in metalliferous veins, which may reasonably be conjectured to be such portions of the original fissures as have not, owing to local causes, been filled up in the same manner as the remainder. These cavities are very irregular both in size and form, but yet, in their size, appear to bear some relation to that of the vein in which they are situated. They are probably the secret laboratories in whica nature has perfected some of the most beautiful productions of the mineral kingdom. The whole of their interior is generally lined with various substances, often crystallized in Metalliferous veins, and, indeed, metalliferous deposits generally, are found traversing a great variety of rocks stratified and unstratified, and appear to belong equally to formations of igneous and sedimentary origin. Although not confined to that class, they may be said to exist most abundantly in the older and more crystalline rocks, and usually in those bordering upon mountain chains. They are mostly found in those situations where a junction occurs between two contiguous rocks; where different rocks are interstratified, or where they are broken or dislocated by faults and cross-courses. Thus, in Great Britain, the tin and copper mines of Cornwall and Devon are situated in granite and different varieties of slate, belonging chiefly to the primary class, and are most productive near the junction of these strata. Many of the metalliferous deposits of Wales and the north of England, producing both lead and copper, are also contained in slaty rocks, which are generally referred to the grauwacke series. Our great deposits of lead, however, are contained in the lower rocks of the carboniferous series, which is the case in the lead mines of North Wales, of Derbyshire, Yorkshire, and the great lead mine district of the north of England. Above the carboniferous series no metalliferous deposits of any value occur in this country. The metalliferous deposits of Scotland occur in primary and transition rocks; and those of Ireland occur mostly in granite, mica slate, and clay slate, although extending also into the carboniferous series. The mining district of the west of England may be considered to commence at Dartmoor, and terminate at the Land's End. The surface is gently undulating, the loftiest hills rarely exceeding 1000 feet above the level of the sea, whilst the greater number of them range from 500 to 700, and the plains at their bases are usually from 100 to 200 feet above high water. The highest peaks are for the most part granite, whilst the lower hills and most of the plains consist of various descriptions of slate. The granite may be considered to present six patches of large dimensions, as Dartmoor, &c.; and three eminences of Minor dimensions, in which we include St. Michael's Mount. All the other parts of Cornwall (except the Lizard district, which is composed of serpentine) may be said to consist of slate of various kinds The granite is commonly coarse-grained, and of porphy retic structure; the slates, in general, partake of the character of felspar, and are of a compact structure when near the granite, and otherwise when at greater distances. Both the granitic tracts and the slates in their vicinity are intersected by veins or dykes of a porphyretic felspar rock, provincially termed elvan. These dykes or veins have, in a few cases, been traced for miles, and they pass uninterruptedly through both granite and slate; their usual direction is about 20 degrees south of west, and they are generally several fathoms in width. The sulphuret of zinc (blende, or the black jack of the Cornish miners) occurs very abundantly in the mineral veins of Cornwall, being, however, more frequently associated with the ores of copper than those of tin. The conditions favourable to the production of tin and copper lodes have been favourable also to the appearance of the sulphuret of zinc or blende, which, however, fre quently occurs in the continuation of tin or copper lodes, far beyond those localities where the tin or copper can be profitably raised. Viewed on a large scale, blende is one of the most widely distributed ores in Cornwall. while the carbonate of zinc, or calamine, is a very rare one in this district. The sulphuret of zinc is not, however, an ore much worth raising at present for profit. Cobalt is a rare ore in this district, and does not seem to be accompanied by any marked geological conditions, as far as regards its occurrence in any particular class or kind of rock. The same may be said of bismuth; and nickel is a very uncommon metal too, and has only been found in any workable quantity near St. Austell. The Siloci of Devon and Cornwall has for the most part been obtained from those ores of lead (argentiferous galena) in which its presence has been detected. Silver ores-proper have, however, been obtained in several mines, in lodes or cross-courses in the grauwacke. Such ores have consisted of native or pure silver, and silver in various states of chemical combination with sulphur, arsenic, &c. MINING OPERATIONS. Preliminary Proceedings. When the mineral contents of a spot are entirely unknown, the operations instituted for the discovery of lodes must be founded upon the general presumptions furnished by geological science in connection with mining experience, as mineral deposits usually present no precise traces of their existence at the surface. The first objects of pursuit, in such circumstances, to the Cornish miner, are what he denominates shode or shoud-stones. These stones are partially rounded and apparently waterworn, and are found on the surface or at very small depths below it. Their mineralogical characters nearly resemble those of the contents of the lodes in the vicinity, of which they are presumed to be portions removed by diluvial action. As, however, the shoad-stones contain tin ore, a careful search for them has been constantly kept up, and their increasing scarcity will probably render this mode of discovery impracticable. When they were uncollected, the examiner might commence marking their presence at any given spot, and then trace them to where they appeared in the greatest abundance, which situation was probably the nearest position of the lode itself. Upon arriving at this place, he would cut trenches, or dig little shafts, to ascertain how far his suspicions were well founded. Should the precise situation of the vein, whose existence has been ascertained by tracing the shoad-stones, or by any other mode be unobservable, it may be asccrtained by opening trenches in the alluvial soil, deep enough to expose the solid rock; their direction being at right angles to that in which analogy, or the position of other veins in the neighbourhood, would render it probable that those in question should lie. Supposing the direction of the vein, and its dip or underlie, to be ascertained either by the shoding, and by sinking a few shallow pits upon it, or by previous experience in some adjoining mine, the further exploration may be continued either by sinking upon its course from the surface, or by forming a horizontal passage to intersect it, which is commenced from a valley, or the lowest point in the neighbourhood, and is called an adit. This last plan, however, being both slow and costly, is seldom adopted, unless there is a tolerable certainty of its results being highly favourable. The mode of proceeding is in a great degree dependent upon the means and prospects of the undertakers, and upon the commercial arrangements and pecuniary resources of the mining company. The lode and its directions being discovered by the means above detailed, the next point is to determine the site of the shaft upon some convenient spot of ground. If the shaft is to be sunk in an inclined direction upon the course of the vein, which is frequently desirable, the site is not so circumscribed as when it is to be sunk perpendicularly upon it. In the latter case, the shaft is necessarily commenced upon that side towards which the vein inclines or underlies, and at such a distance from its appearance at the surface (or outcross) as to cut the vein at a premeditated depth, which may be from ten to thirty fathoms, in accordance with the means of the adventurers, and with their knowledge of the quality and conditions of the lode, the upper portions of which are seldom productive. The vein being cut, the shaft may be continued either perpendicularly, and through the vein, or obliquely, and in the course of the vein. Should the lode be expected to turn out excellent and profitable, the former plan will be adopted, as it will be ultimately the most advantageous, and will enable a large mine to be carried out. But if the lode is questionable, and the means of the miner the same, the latter course will be proceeded upon, as it is far the cheaper one as well as the speedier. In driving the second and the succeeding levels, it is clear that the further we proceed from the shaft in each direction, the greater will be the closeness of the air, and the more essential will ventilation become. It is then that small shafts, called winzes, are sunk. Thus a communication is opened between all the levels, each one of them possessing winzes opening upwards from itself to the next superior level, and also others opening downwards from itself to the next inferior level, by which means a double communication with the atmosphere and every level is effected, and an ascending and descending current of air produced. But in addition to their utility for the purposes of ventilation, winzes are equally necessary to the working out of the ore from the lode, and, indeed, are advantageous in trying its value. Unless little or no ore has been discovered upon the opening of the first level, winzes will be commenced at a very early stage of the mining operations; and when the ore is found to be tolerably good, they will be opened at intervals of twenty or thirty fathoms in each level. Their position will be especially determined, so as to prove the richest and most promising parts of the vein, and to avoid those hard and unproductive portions which may be. supposed to be unworthy of exploration. As far, too, as it can be effected in accordance with these views, the position of the winzes will be such as that each of them may come about mid-way between the nearest two above it. The system of works, therefore, by which the lode is explored and the mine established, is not unlike a system of masonry, if the horizontal joints of the stone work be supposed to represent the levels, and the vertical joints the winzes. When, by these arrangements, the lode has become divided into a number of solid rectangular masses, as just described, the mine will have been brought into an effective state of working, and parties of men will be set to raise ores from all the most productive points. Where the vein is not very hard and stubborn, the ore may be broken down with the pick only, but it is generally necessary to blast the rock with gunpowder, by which mode large quantities of ore are detached at every “shot." In working the ores either by the pick or the blast, the men usually work upwards, from the upper part of one level towards the bottom of the one above it; and the excavations are so arranged that the ore may readily fall down to the level below them, whence it is carried in train wagons to the nearest point of the shaft, and is thence raised to the surface. Tools-Excavating Processes. The principal tools used by the miners are picks for working the rocks, and borers and mallets for making the holes for blasting. These are often sent up and down in the bucket in which the ore or rubbish is drawn to the surface, but the miner very commonly carries with him from ten to twenty pounds' weight of tools. A constant necessity exists for hardening and sharpening these tools which is done at a smith's shop above ground, though it would seem more advantageous to establish a forge under ground, as has been done in one Cornish mine only, but with considerable economy; such subterranean forges are more common in Ireland, two having been in use for several years in a mine in the county of Cork. The great body of the miners under ground are employed in excavating the rock, whether for the sinking of shafts, the driving of levels, or the removal of the pieces of ore from the lode. These operations require, in most of the mines, the almost constant occupation of the explosive force of gunpowder. A great part of the work, therefore, consists in "beating the borer;" that is, driving an iron cylinder, which terminates in a wedgeaped point, by blows with a heavy hammer (mallet), hilst it is turned by another hand. The necessity or advantage of making the hole in a particular direction, often constrains the miner to assume every variety of posture in carrying on his work. When the rock has been bored to a sufficient depth, the charge is introduced, and rammed down with a tamping-iron, a particular clay being used as wadding, and a certain length of safetyfuse keeping up the communication with the powder; fire is applied to this, and the miners retire till the explosion has taken place. It is not often that the safetyfuse misses fire, but accidents now and then arise from the impatience of the miner leading him to an imprudent examination of the fuse when it burns more slowly than usual, which may occur from tight ramming down. Safety-fuse is a kind of cord, into the texture of which gunpowder is introduced, and which is afterwards covered with a coating of a bituminous nature-the process being secured by patent. Previously to its employment, frequent accidents occurred to the eyes of the blasters, but such calamities are now rare in comparison. The form of the tamping-wedge, and the metal of which it is made, are of great importance, more especially the latter, as it is obvious that any metal, the friction of which shall produce sparks, is excessively dangerous. In the great lead mines of Northumberland, we lately found that the use of copper prickers and beaters has been adopted to some extent in blasting, but certainly not to so great an extent as necessary. Wherever copper tools have been employed, no accidents have occurred by sparks flying from the needle. The pick is a very useful tool, and one very much employed by the miner both in working in the rock and in breaking down ore, where the ground is not so hard as to require blasting. It resembles a common pick-axe, but is smaller and more convenient, the iron head being sharp and pointed at one end, and very short and hammer-shaped at the other, a form which peculiarly adapts it for under-ground employments. The wedge, or gad, made of wrought iron, and often with curved sides, is sometimes used, together with the pick. The borer, or jumper, is an iron rod or circular bar, commonly about two feet long, and steeled and formed into a flat sharp edge at the end, which is driven into the rock, as before said, while a person turns it round, so as to expose the cutting edge to fresh surfaces of rock; the pulverized matter is drawn out from time to time by a scraper, and the charge is introduced when the hole is fully perforated. Working. in those worked upon a By these processes, the workings of the mines have become so extended as gradually to lose their original simplicity. When the levels have been extended to a considerable distance from the shaft, the ventilation will again be found defective, notwithstanding the frequent communications by winzes; for the greater the distance the current of air is carried, the more feeble it plainly becomes. This deficiency is still further augmented by the increasing number of the men now employed in the works, the presence of a great number of candles, and the smoke resulting from the larger employment of gunpowder in the process of blasting. The expense, too, of the transport of ore and masses of rubbish to the shaft, is, on account of its greater distance, much more considerable. To add to these, we have the greater expenditure necessary for the drainage of the water from the mine, and for the support of its passages and roofs by timber. In order to obtain a clearer idea of these several matters, we shall consider them separately, and speak first of the shafts. In addition to the circumstances just named, the irregular distribution of the metalliferous portions of the lode will cause inequality in the workings, and will, with the other matters, render the sinking of one or more shafts indispensable. Again, when the depth becomes very considerable, many of the first shafts are rendered in a great measure useless, either from their being inclined, and thus inconveniently circumstanced for machinery, or from having cut the lode at a shallow depth, and thus requiring cross-cuts progressively, longer in proportion to the increase of the depth and inclination or distance of the lode from the shaft. Hence, in very deep mines, a double line of shafts will often be found to range along the course of the principal veins; and sometimes even three shafts will be found placed opposite each other, and intersecting the same lode successively at increased depths. In such cases as this, while the most recent shafts are used for drainage and the extraction of the ore and It is judged most expedient in mines, more especially masses of rock, the older and more shallow shafts are A mine in a complete working condition exhibits a most extensive series of operations, in connection with the shaft, the lifting and descending by ropes and pulleys, the drainage, the excavation, the ventilation, &c. At the bottom of the shaft, and in the various stages in which the excavations are going on by the miners, in their attempts to follow the lodes, the operations are on a scale which seldom fails to surprise the stranger. |