MINE. 



333 



;. of by a day-level, or by machinery ; and while the coal 

 ; - laid dry by this winning is working, a deep day-level is 

 progressively bringing forward, which, as soon as it in- 

 tersects the coal, and communicates with the engine 

 level, supersedes the use of the engine. 

 Offtake these levels, which drain coal-fields of water, 



WteU. and render them workable, there are other levels of more 

 limited operation, used in mining. These are named off- 

 take drifts. The object of these is, that when 

 a coal is to be won by an engine, the mouth of the en- 

 gine pit is so situated as to the ground adjoining, that, 

 at a moderate ezpence, a level can be brought up to in- 

 tersect the engine pit a number of yards under the sur- 

 face, so that the water of the mine, in place of being de- 

 livered at the surface, is discharged into the off-take 

 drift. The lower down this kind of level, or off-take 

 drift can be procured with ease, the greater will be the 

 advantage in lessening the column of water to be lifted 

 in the pumpi by the engine. From 20 to 30 fathoms 

 off-take is a considerable object, as that depth saves 

 what is termed a lift of pumps ; even 10 fathoms off- 

 take is of consequence to have. These levels are not 

 only of use in lessening the load of water on the engine, 

 but if coals are intersected by them, they will intercept 

 all the crop water to the depth of the point of inter- 

 section, and prevent it from going down upon the dip 

 part of the coal, where it would be a heavy load on an 

 engine, if after intersecting the engine pit, the level is 

 carried forward till it intersect the coal.i, through which 

 the pit is sunk, all the crop water of these upper coals 

 will also be intercepted. Such levels are not only of 

 use in the winning described, but if anew deep winning 

 is made to the dip, the crop water is not only prevented 

 from descending to the pit bottom, but the advantage 

 of discharging the water raised by the engine into the 

 level is also obtained. 



The most prominent advantages being thus stated, 

 regarding day levels, we have now to state the manner 

 in which they are executed. 



9tj itttU. As, before the discovery of the steam engine, the coal- 

 fields which could be drained by hydraulic machinery 

 were comparatively very limited in number, and as the 

 draining of water by men or horses was not onK 

 expensive, but very limited as to the depth at which 

 water could be raised, the driving of day levels was a 

 primary object with the early miners; and we are as- 

 tonished when we survey the works of this kind execut- 

 ed by them both as to depth and extent, and that be* 

 fore the application of gunpowder to the blasting of 

 rocks. \Vithout this powerful auxiliary of the i 

 t is not easy to comprehend the extreme labour, and 

 patient perseverance required to pass through the very 

 hard rocks which were met with. Thi teems to be 

 the cause of the levels executed in the early periods of 

 mining being of so small a size that a man has just 

 room to creep through them. 



iy of the levels of the present day are only three 

 feet in width, and four and a half in height. Although 

 these dimensions are in general sufficient to carry off 

 the water which may be found in the colliery, they 

 are too small when the mine is to be repaired, or when 

 sediment and obstructions gather in them. They ought 

 not to be less than four feet wide, by five feet six inches 

 or six feet high ; this is abundantly large for carrying 

 off water. But there are some day-levels which' not 

 only are driven for carrying off the water, but as a pas- 

 the same time for bringing out the coals from 

 the mine. In this case, the width would require to be 

 at least four feet six inches, or five feet, so as to admit 



4 



of an iron rail- way to be laid in it; besides which, there 

 require to be, at proper distances, wider places formed 

 in the side of the mine, to allow the loaded and empty . 

 carriages to pass each other. These by-pass roads are C0 j 

 regulated as to the distance from each other, according 

 to the quantity of work to be performed. When a day- 

 level thus serves a double purpose, the water is either 

 conducted in a covered drain, cut deeper than the sole 

 on which the rail-way is laid, or it is conducted along 

 the side of the rail- way. 



In other instances, a day-level is not only made to 

 carry off the water from the colliery, but is constructed 

 of such size as to form a canal, by which boats can be 

 carried into the coal mine, and loaded for the market. 

 These levels are of various dimensions, according to the 

 extent of traffic calculated upon. The smaller kind is 

 nine feet wide, by nine feet nigh, having from three to 

 three feet and a half of water in depth. The larger di- 

 mensions in practice are nine feet wide, twelve feet 

 high, with five feet depth of water. 



In driving a common day-level, for the sole purpose 

 of draining the coal, the point having been fixed for 

 commencing it, if the ground is flat, part of it at first 

 will be executed as an open cast or ditch, securely laid 

 with flag stones in the bottom, and built in the *i,ln 

 with sufficient stone walls. The sole to be conducted 

 in a line as nearly level as possible. If the alluvial cover 

 continues, and becomes too deep for open cast, the mine 

 or level must be arched, and the work conducted under 

 cover. If the alluvial cover is soft, it will require to b 

 secured in the sides and roof with timber, which can 

 be drawn out, and used again, if the nature of tin- 

 case admits of this being done ; but if this is not the 

 case, the timber must be so placed as to admit the 

 fide walls and arch to be built within it. In this way 

 the level is carried forward until it has proceeded some 

 yards under cover of the rocks, or strata of the coal- 

 field, when, if the strata are strong, no more mason- 

 work is required. The next point is the proper line of 

 direction, so as to reach the coal to be drained in the 

 shortest distance. This line is that of the true dip and 

 rise of the strata ; and that the mine is going correctly 

 in this line is known when the divi icii* of the strata 

 seen in the forehead of the mine, are parallel to the 

 sole of it, which ought always to be level. If the strata 

 form an angle with the sole of the mine, the direction 

 is going oblique to the line of dip; and the greater this 

 obliquity, the greater will be the protracted distance, 

 before the coal can be intersected. In all cases where 

 the strata are not soft and friable, the roof of the mine 

 is cut in an arched form, which adds considerably to its 

 strength ; and wherever the strata are soft and friable, 

 or where the level passes through slips and disloca- 

 tions, the sides are built up, and the roof arched with 

 stone or bricks. The latter are generally preferred, 

 on account of their occupying less room, are easily car- 

 ried into the mine, and the work more cxpeditiously 

 executed ; it being a rule that the mine snail, in all 

 such cases, be made of such a size as to admit the build- 

 ing, without narrowing the fixed dimensions of it car- 

 ried through the rock. As a day-level proceeds for- 

 ward, the air begins to fail, from the breath of the 

 workmen, the use of gunpowder, and the issue of 

 carbonic acid and hydrogen gas, which are sometimes 

 found in great abundance ; to remedy this, deal boxes 

 or pipes, from eight inches to a foot square, are carried 

 in from the mouth of the mine to the forehead, and 

 lengthened as the mine proceeds. This generally pro- 

 duces a sufficient circulation of air, until it ii found nc. 



