350 



MINE. 



PLATB 



Mine of a regular and uniform thickness of pillar. If the pil- 



^^Coal. l ars are formed without attending to the above plan, 



Working" tne ' r sides will intersect through the backs and cut- 



ofcoal. ters obliquely; and when the weight begins to bear 



up -n them, and are winded by the air passing 



through the waste, large wedge-shaped pieces of coal 



fall off. 



It frequently happens that the dip-head level, in its 

 course, intersects the cutters at a very oblique angle. 

 In this case, when rooms and pillars are set off, the 

 face of the pillar and width of the room, must be mea- 

 sured off an extra breadth in proportion to the ob- 

 liquity, as in Fig. 15. Plate CCCXCI. Without at- 

 eccxci. tention to this, rruch confusion and irregular work is 

 produced ; on which account, the pillars are always 

 formed much larger than in the common workings ; 

 besides, it is a general rule to make the first set of pillars 

 next the dip-head level, even where there is no obliqui- 

 ty, much stronger, in order to preserve the dip-head 

 level from being injured by any accidental crush of the 

 strata. 



Having thus described the manner of arranging the 

 rooms and pillars the various systems of working coal 

 have now to be explained. 



Jig. 13. Fig. 1 :i. shews one of the simplest modes of working 



coal. A is the engine pit, B the bye-pit, or No. 2. pit, 

 CD the dip head levels, always carried in advance of the 

 rooms, E is the rise or crop mine, also carried in ad- 

 vance. '1 hese mine* not only open out the work for 

 the miners in the bed of coal, but, by being in advance, 

 give plenty of time for any operation which m;>y be re- 

 quired, if these mines are obstructed by dikes or hitches. 

 In fiis example the rooms or boards are wrought from 

 . the dip to the crop ; the leading rooms, or those most 

 in advance, are those on each side of the crop mine E : 

 all the other room follow in succession, as represented 

 in the figure ; consequently as the rooms advance to the 

 crop, additional rooms are begun at the dip head level, 

 towards C and 1). If the coal is found to work better in 

 a level conrsedirf ction, then the leading rooms are next 

 the dip-head level, and the other rooms follow in suc- 

 cession. In this manner, the rooms are carried a crop- 

 ping in the one ca*e, till the coal is cropped out, or is 

 no longer workable ; and, in the other case, they are 

 extended as far as the extremity of the dip head level, 

 which is cut off either by a dike or slip, or by the boun- 

 dary of the coal-field. As to additional pits, these are 

 placed at such distances from each other, as will best 

 suit the economy pursued in working. When the 

 winning is under 6'0 fathoms in depth, and the sinking 

 of pits is of little expence, they are numerous ; but when 

 they are deep, and attended with very great expence, 

 one shaft divided into two or more pits can be made to 

 work out a very extensive coal-field. 



System ' n verv deep winnings of from 80 to 200 fathoms in 



pursued in depth, the first workings are carried forward with 

 deep win- rooms, pillars, and thirlings, but under a very different 

 aingj. arrangement, both on account of the great depth of the 

 superincumbent strata, the enormous expence laid out 

 in sinking a pit, and the order, regularity, and strict- 

 ness of discipline indispensibly requisite for ventilating 

 the mines, preserving the lives of the workmen, and 

 prosperity of the whole establishment. In these deep 

 winnings, the same general system is followed, as stated 

 regarding dip- head levels, and crop mines, excepting 

 those peculiarities connected with the ventilation, which 

 will be treated of separately. In the early practice of 

 working deep collieries, the system was to work with 

 pillars considerably stronger than was conceived neces- 



sary for supporting the strata, in order that when the Mine, of 

 workings were carried on to the full extent proposed, Coal, 

 the workmen might begin with the pillars at the greatest v ~r~~ ' 

 distance from the pit bottom, and either work a cer- * 

 tain proportion from each, securing themselves from the 

 falls in the roof by prop- wood, or they sometimes 

 wrought the heart out of a pillar either in the one di- 

 rection or the other, and sometimes in both directions. 

 Though the size of the pillars, and general arrange- 

 ment of the work, were laid out with the view of tak- 

 ing out a great proportion of the pillars ultimately, yet 

 it frequently happened, that, before the workings were 

 extended to half the proposed extent, some part of the 

 work gave way, and produced a crush ; but the most 

 common misfortune was the pillars sinking into the 

 pavement, and deranging the whole economy of the 

 work. When either a crush or creep commences under 

 such a depth of strata, it is almost impossible to stop its 

 progress ; the pillars thus sunk into the pavement are 

 lost. But if a crush or creep did not take place during 

 the working of the colliery, and the working of the pil- 

 lars commenced, a crush or creep is expected very soon 

 to come upon the weakened pillars. In this case it 

 frequently has happened that the pillars, in their entire 

 state, had not strength to keep back the crush, and 

 therefore it overran the pillars, making the workmen 

 abandon the work, and escape for their lives. In this 

 manner, also, much coal was lost. If the crush or creep 

 was not so violent as this, it frequently was resisted for 

 sometime by the strength of the pillars, but it was im- 

 practicable to resume the work close to the creep ; and 

 therefore a great breadth and stretch of pillars had to 

 be left as a barrier betwixt the crush and the next set 

 of pillars which was to be wrought. In this manner 

 were collieries carried on, and an immense proportion 

 of the coal lost for ever. This loss amounted in many 

 cases to no less than a third, and, in some instances, 

 even to a half of the whole area of the coal-field. This 

 great loss of coal was not only making an uncommon 

 sacrifice of mineral property to the mine-owner, and 

 to all concerned in the working of it, but the loss was 

 great in a national point of view, as the coal tl us left 

 under-ground was lost to all generations. An im- 

 provement, therefore, in the system of working deep 

 mines became a great desideratum, and many plans 

 were brought forward by mining engineers of the 

 greatest experience. 



Besides the loss of coal by the system before men- 

 tioned, there was another great evil which required 

 also to be corrected. In carrying on the workings of 

 an extensive colliery or coal-field of one or more hun- 

 dred acres, the whole area or extent of the coal-field 

 was one continued range of rooms and pillars, com- 

 municating with each other without any divisions or 

 barriers of coal left across the workings, excepting 

 when formed to counteract a crush or creep already 

 begun, or to strengthen the waste adjoining a slip or 

 dislocation of the strata; the consequence of this sys- 

 tem was, that if a crush or creep began when the 

 workings were much extended, they over-ran very 

 frequently the whole of the pillars, and were only re- 

 sisted by the whole coal at the wall faces, so that the 

 ventilation was entirely deranged, the roads leading 

 from the wall faces to the pit bottom shut up and ren- 

 dered useless, and the recovery of the colliery by 

 means of new air courses, new roads, and opening up 

 of the wall faces or rooms, attended with uncommon 

 expense and danger. Even when the pillars stood 

 well, this system had other very great inconveniences 



