MINE. 



S49 



Working 

 fowl. 



' ex penencc, 

 bett systitn can 



Mine* of that i, whether it is firm and strong, m rery weak, 

 ' and liable to rail down ; also the kind of superincum- 

 ~~ bent strata, whether strong or tender. 



5th, The kind of alluvial cover, whether of a dry 

 nature, or composed of quicksands and much water 

 upon the rock head. 



6M, The situation of rivers or collections of water 

 connected with the coal field, particularly if these are 

 Bear the crop of the coal*. 



7/A, The situation of towns, villages, and mansion- 

 houses upon the coal field, whether they are likely to 

 be injured by any mode in which the coal is proposed 

 to be wrought, having in view the thickness of the 

 strata betwixt the surface and the coals to be wrought, 

 also the thickness of the bed or beds of coal. 



When coal-fields have been wrought in a district of 

 country for a considerable period of time, the expe- 

 rience gained by the miners directs them how to pro- 

 ceed in similar circumstances, and therefore, in mines 

 opened op in new districts, it i* difficult to lay down 

 specific rules for the very various circumstances con- 

 nected with a coal-field ; and although general rules 

 may be laid down, it may require year* of ex) 

 and the trial of many mode*, ere the 

 be determined upon. 



Emtral The following general rules are ueful in determin- 



ulc*. ing the mode of working coal. 



lr, If the coal, pavement, and roof are of ordinary 

 hardness, the pill irs and rooms mny be proportioned 

 to each other, corresponding t the <l> pth of the su- 

 perincumbent strata, providing all the coal proposed 

 to be wrought is taken away by the first working, as 

 in the first system; but if the pillars are to be wing- 

 ed afterwards, they must be left of an extra strength, 

 as in the Sd system. 



Sst, if the pavement is soft, and the coal and roof 

 strong, pillars of an extra ise must be left, to prevent 

 the pillars sinking into the pavement, and producing a 

 deep. 



id. If the coal is very soft, or has numerous open 

 barks and cutters, the pilUrs must be left of an extra 

 sixe, otherwise the pressure of the superincumbent 

 strata will make the pillars fly or break off* at the backs 

 and cutter*, the result of which would be a total de- 

 struction of the pillar*, termed a crush or sit, in which 

 the roof sinks to the pavement, and closes up the 

 work. 



4th. If the roof is very bad, and of a oft texture, 

 pillar* of an extra sise are required, and the rooms or 

 boards comparatively very narrow. 



In short, keeping in view all the circumstances be- 

 fore mentioned, it may be stated generally, That when 

 the coal, pavement, and roof are good, any of the sys- 

 tems before mentioned may be pursued in the work- 

 but if they are soft, the plan ii to work with 

 rooms of a moderate width, and with pillars of great 

 extra strength, by which the greater part of the coal 

 may be got out, nt the last of the work, whr n the mi- 

 ners retreat to the pit bottom, and there finish the 

 workings of a pit. 



When pilUnare left having too small a base, though 



abundantly trong in themselves, but resting on a soft 



pavemen' cnnteqttence is, their sinking into 



the pavement by the weight of the superincumbent 



i, which produces n creep over all the workings, 



and has the effect of shutting up the roads, destroying 



ptATt *h* <r courwM, and deranging the whole economy of 



teem. ' 1lier J operations below ground. Fig. 10. Plate 



Ftp. 10. A CCCXCI. represents the effects of pillars sinking in. 



to the pavement, and producing a creep. Fig. 11. Mir.** r 

 represents large pillars, and a room, with the roof 

 stratum bending down before it falls at a. Worf 



With regard to the proportions of coal wrought, to of o a | n ' 

 the area left in pillars for support of the superincum- 

 bent strata, where all the coal intended to be wrought 

 from a given area is taken at the first working, it 

 ries from four-fifths to two-thirds ; and in a general 

 view these are about the proportions in the present Proportion 

 practice pursued under the system, when the depth of coal 

 does not exceed 70 fathoms ; but as the losing of a wrought, 

 third of the whole area of coal is a great proportion, 

 the superior mode of working, as stated in the 3d sys- 

 tem, ought to be adopted. 



The rule for calculating the proportion of coal 

 wrought to the area left in pillars, is as follows: It 

 !* termed calculating the proportion wrought of a win- 

 ning. Fig. 12. represents a small portion of the pil- p tiT i 

 lars, rooms, and thirlings, formed in a coal-field, a a cccici. 

 are two rooms, / the pillars, i the thirlings. Sup- *"> !* 

 pose the rooms 12 feet in width, the thirlings tin- 

 same width, and the pillars 1'2 feet on each side. Add 

 the nice of the pillar to the width of the room, = J t , 

 add also the end of the pillar to the width of the thir- 

 ling, = ?4, then 21x2+ = 570' then the area of the 

 pillar, l_'x 12=144. And a* 576, divided by 14+, 

 1. the result is, that a fourth of the coal is left 

 in pillar*, and three-fourths wrought out. d, t,f, g, 

 is one winning, and p, t, k, h another. From an in- 

 spection ot the figure, the workings of a coal-firld, if 

 regular, resolve themselves into quadrangular areas, 

 having the pillar situated in one of the angles. 



As the back* in the coal do not generally lie at right 

 angles to the dip and rise of the coal, but rather ob- 

 lique to that line, the rooms or boards arc begun or 

 broken off at the dip-head level, so that the luck* of 

 the coal cross the sides of the boards at right angles. 

 This by some i* termed working right upon the plane 

 of the coal, others term it right upon the web ; but if 

 cutters are more distinct and open than the backs, 

 then th. it direction is termed the plane, and the boards 

 are said to be wrought upon the end plane, or simply 

 un the end, or in a level- course direction. 



In forming the pillars, and carrying forward the Formation 

 boards with regularity, particularly where the backs of pillars, 

 and cutter* are very distinct and numerous, it is of im- 

 portance to work the rooms at right angles to the 

 backs, and the thirlings in the direction of the cutters, 

 however oblique these may be to the backs, as by this 

 plan the rooms are conducted with the greatest regu- 

 larity with regard to each other, kept equidistant, 

 and the pillars of a given area arc the strongest when 

 formed by this mode of working. 



At the same time, it must be understood, that it sel- 

 dom happens that a back or a cutter is found exactly 

 at the place where a pillar is formed ; but that is of 

 no consequence, as the shearing or cutting made by 

 the miner ought to be in a line parallel to the backs 

 and cutters. This precise system is particularly ne- 

 cessary, where pillars are formed ujifti the calculation 

 of just supporting the superincumbent strata, or when 

 they are made a little stronger, to be winged after- 

 wards. This precifencss is dispensed with where im- 

 mense pillars or walls of coal are left in the first work- 

 ing, with the view of taking out the whole afterwards. 

 At the same time, even in this system, the working of 

 the rooms with their sides parallel to the cutters, is the 

 best method of keeping all the rooms at equal distan- 

 ces from each other, so that betwixt each there may be 

 7 



