diamond drilling was commenced. When the diameter of the hole was 2 inches, and the diameter of the core brought up 13 inch, 4406 feet of rods fell to the bottom and became jammed in that portion of the hole that was unlined, and so led to its abandonment. Boring commenced on January 26, 1892, and on May 17, 1893, had reached a depth of 65726 feet, the final 3:28 feet having taken over 3 months to finish. The actual boring occupied 399 working days, with a daily advance of 16:4 feet. The total cost was £3760, or about 115s. per foot, which compares very favourably with that of Schladebach, where the cost was 37s. per foot. Surveying Bore-holes.-The great difficulty in boring is to keep the holes truly vertical, and, in spite of all efforts to the contrary, crooked bores are common, especially where the beds are inclined. No rules can be given; the only thing to be done is to exercise the greatest care. Unfortunately, bore-holes, by all the methods, are liable to deviate from the perpendicular, the diamond drill, which was assumed to always bore a perfectly straight hole, being no better than any of the other systems. However, if an accurate survey be made, a crooked hole gives just as valuable information as a straight one. In the method devised by Mr. E. F. Macgeorge,* clear glass phials filled with a hot solution of gelatine, and each containing in suspension a magnetic needle and a very delicate plumb-bob, are lowered into the bore-hole and allowed to remain there until the gelatine sets, when they are withdrawn, and by means of a special instrument the angles of the compass and the plumb-bob are noted. Another suggestion † is to lower into the bore-hole glass cylinders containing hydrofluoric acid, which etches a line on the glass. Both these methods are reviewed by Mr. B. H Brough, who gives a full description of the instruments employed and the way of using them. The Uses of Bore-holes in Mines are many and valuable. Every colliery ought to be provided with a set of tools, and men instructed in their use. (a) Tapping Water.-A provision of the Coal Mines Regulation Act, 1887, is to the effect that all roads approaching old workings, where there are likely to be dangerous accumulations of water, should be preceded with bore-holes. One bore-hole is usually kept straight ahead for a distance of about 5 or 6 yards, and flank-holes, at an angle of 45° with the centre line of road, are put out for a similar distance on each side. The general practice with the leading hole is to bore in a certain distance, and then remove part of the face, a further length being then bored before any more ground is removed. In this way, the distance from the face to the back of bore-hole is never less than 5 yards. Where water is expected, plugs should be kept in readiness to drive in immediately it is released; or if the pressure is likely to be great, it is best to bore through a length of pipes fitted with a tap. Such pipes and tap may be wedged in position in several roughand-ready ways, but to minimise the risk of their being blown out when the old workings contain water or gas under considerable pressure an elaboration of the ordinary apparatus has been patented by Mr. J. * Engineering, xxxix., 260 (1885). + Translation by C. Z. Bunning and J. K. Guthrie, N.E.I., xxix., 61. * Cowey (Fig. 39). A hole is first drilled for a few feet into the coal, and a tube, a, inserted in it. The inner end of this tube is fitted with an india-rubber sleeve, b, projecting slightly beyond the tube end and prevented from slipping back by a collar, while the outer end of the tube is provided with a flange which presses against a rubber ring, c, on the edge of the bore-hole. The pipes outside the bore-hole are screwed into this flange; d is a cross piece fitted with a pressure gauge,e, and dip pipe closed by a valve, f, through which the débris, water, or gas passes away. The thread of the feed screw h passes through a gun-metal sleeve nut, i, tapped to receive it. This is attached to the tubes through which the boring tools pass by a modification of the ordinary bayonet joint, a front view of which is shown. The whole apparatus is secured to a timber frame by two clamping plates, k, which by means of bolts forces the tube a and its india-rubber sleeves into close contact with the front and inner end of the hole. Mr. G. Burnside † has also introduced an apparatus similar in most of the details to the preceding, but differing from it in the way the stand pipe a is locked in the bore-hole. He employs two supporting plates round the tube and two wedges. The latter are inserted with their larger ends inwards, and when everything is in position they are drawn outwards by stretching screws, binding the supporting plates against the sides of the hole and the tube, and firmly locking the latter in position. Where abnormal pressures are likely to be encountered, either of the above methods are probably safer than the general one of simply wedging the stand pipe, but the latter acts satisfactorily in the majority of cases. (b) Releasing Gas.-In collieries liable to sudden outbursts of firedamp, bore-holes are systematically put out of the working places into the layers of strata in which the gas accumulates, in order to drain it out gradually. At Wharncliffe Silkstone, and other collieries where this procedure is adopted, it has met with success. * British Patent, No. 311, 1891. + Ibid., No. 2299, 1891. (c) Proving Faults.-Bore-holes are of the greatest assistance in determining the amount of throw of faults, and have saved considerable sums of money, which would otherwise have been spent in unprofitable exploratory work. With their aid one can determine the gradient required to drive the roads that will intersect the dislocated seam. Especially is this the case where the hade of the fault is vertical or ill-defined, as they actually prove in such instances, whether it is an upthrow or downthrow. Owing to the confined space in roadways, the cost of boring is rather high, as much time is wasted in screwing and unscrewing rods. From a number of cases carried out under the author's direction the cost per foot averaged 4s. for distances bored of about 30 feet, with diameter of hole 3 inches, the rate of wages paid to men being 5s. 6d. per day of eight hours. The cost of boring uphill seems less expensive than downhill, if the weight of boring tackle is counterbalanced, as the disadvantage of clearing out the hole and unscrewing of rods for such purpose is removed. (d) Steam and Rope-ways. The anthracite region of Pennsylvania supplies numerous instances of the employment of bore-holes for steam and rope-ways passing from the surface to the interior of the mine.* At Shenandoah City slope, an 8-inch hole was bored by the method employed in the oil regions, and lined with 5-inch casing, through which a rope travels, the space between the casing and the rock being filled in with cement. The engines and boilers are on the surface. Another hole, 6 inches diameter, was then bored, and two lines of 2-inch gas-pipe laid in it, the interstices between being filled in with cement. One pipe is used for a speaking-tube and the other for a bellwire to the engineer at the machinery on the surface. At East Franklin Colliery there are two bore-holes, each 8 inches diameter cased, and cemented, 763 feet deep. These holes are 7 feet apart, and are used to hoist from a double-track underground slope. At Lincoln Colliery, an 8-inch hole is used to convey steam to an underground pump through a 4-inch steam-pipe. As this hole was remarkably dry, it was not cased. At the Clear Spring Colliery, West Pittston, a 6-inch hole was drilled 270 feet, and a line of 4-inch steam-pipes inserted. This hole was not cased, and, owing to the flow of about inch stream of water down it, condensation was so great that the pressure was lowered from 120 lbs. at surface to 40 lbs. at bottom of hole. Afterwards, the space between the rock and the steam-pipe was cemented, and a 4-inch steam-pipe placed inside the 41-inch pipe, with the result that the steam pressure at the bottom of the hole was the same as on the surface. These holes have also been successfully used in dealing with mine fires, for providing water supplies, for stowing underground excavations, and many other purposes connected with mining. Bibliography.-The following is a list of the more important memoirs dealing with the subject matter of this chapter : CHES. INST. Boring and Boring Machines, A. H. Stokes, iii., 192. AMER. INST. M.E. Recent Improvements in Diamond Drills, W. P. Blake, i., 395; The Diamond Drill for Deep Boring, compared with other systems of Boring, O. J. Heinrich, ii., 241; and Supplementary Paper, iii., 183. * School of Mines Quarterly, New-York, ix., 189. N. E. I.: Description of an Instrument for ascertaining the Inclination from the Perpendicular of Bore-holes, C. Z. Bunning and J. K. Guthrie, xxix., 61; On Diamond Rock Boring, T. J. Bewick, xxx., 93. Soc. IND. MIN.: Notice sur les appareils de Sondage employés par la Société Anonyme de Commentry Fourchambault, M. Lecacheux (2e Série), ix., 337; Note sur l'outillage employé dans quelques Sondages du Gard, M. Sarran (2o Série), ix., 453; Sondages des Boubes et de Neuville exécutés à l'aide de la couronne a diamants, M. Baure (2o Série), xiv., 5. So. WALES INST.: On the Machinery used in Boring Artesian Wells, and its application to Mining purposes, W. Mather, iv., 51; Some particulars of Boring with the Diamond Drill, A. Bassett, ix., 130; and Hort. Huxham, ix., 201; Large and Deep Bore-holes with the Diamond Drill, James Barrow, xi., 315, and xii., 41. MID. INST. On the Diamond Rock-drill, J. H. Gulland, iii., 254; A History of Deep Boring or Earth Boring as practised on the Continent, J. C. Jefferson, v., 105, and vi., 29 and 73. FED. INST. Davis Calyx Drill, T. H. Davis, xv., 363. COLLIERY GUARDIAN: Deep Boring on the Canadian System near Friedstadt, Austria, R. Nelson Boyd, lxvii., 897. REV. UNIV. Note sur le procédé de Sondage du système Raky, M. Buhrbanck : (3e Série), xxv., 53. 38 CHAPTER III. BREAKING GROUND. Contracts.-The greatest proportion of the miner's work consists in removing and breaking up different varieties of rock, and to do this various special tools are employed. Usually the different qualities of ground are let by contract to men, and it is here that experience is of the greatest use, as only from that is it possible to judge of the value. Hardness, in a mining sense, is different from the same term looked at from a mineralogical standpoint. Ground that is hard and brittle will often bore better than a softer variety which is tough, because, in the former instance, the blows break off small pieces, while, in the latter, the chisel has to cut its way. Another point is the question whether the ground will "shoot" well, that is to say, whether it contains a number of faces, or joints, which easily break away from the surrounding mass under the action of explosives, or, at any rate, allow the material to be so shaken that it is easily removed by wedging. At one of the collieries under the author's charge numerous intrusions of basaltic rock are met with, and he has adopted a system for judging the value of roading which is worthy of mention. A sample of every intrusion is kept and labelled, with the price per yard paid for driving through it, and, in addition, a microscopical section is cut from the specimen. When other intrusions are met with a piece is broken from each of them, and a section cut and carefully compared with other pieces and sections of which the price is known. From this comparison the price to be paid to the workmen is found. Methods of Hastening Work. The commonest plan of hastening work, and one that gives good results, is to pay the men a bonus for every extra yard they drive over a certain stipulated amount. So far as working is concerned, perhaps, the cheapest way is to only work one shift, for, as a rule, the night shift leave work behind for the day men to do. If different shifts of men are employed the best way is to measure up the amount each shift does, and pay them on it, as by this means each set of men know that they will receive the money for all the work they do, and consequently work harder. Where rapidity is the main object six-hour shifts are adopted, with one workman always remaining to, and starting from, the middle of a shift. This one does all odd work, fetching tools, &c.; the regular workmen are then able to keep constantly at the face. TOOLS USED.-Shovels are principally used for removing broken débris, and always have pointed noses, to enable them to get past the larger pieces of loose stuff. The length of handle varies; commonly it is about 30 inches, this being set at an angle of from 140° to 160° with the surface of plate, which varies from 8 to 16 inches across. In some districts baskets are used for loading in preference to shovels, the coal being raked into them. They are largely em |