34G 



MINE. 



Coal. 



coal. 



Mines of the partings are bad, the coal is said by the miner to 

 have neither roof nor pavement ; and when the cutters 

 . are irregular, the coal breaks in that direction very 

 much serrated, or teethy in the miner's language. 



Besides these chief and regular divisions, there are 

 innumerable cracks and fissures crossing one another, 

 so that when the coals are broken with force, the frag- 

 ments are of a cubic form, particularly in open burn- 

 ing bright coal, named on that account cubical coal, in 

 place of rough coal or cheary coal, as formerly. On 

 the other hand, the coals named splint coals (slate 

 coals) have few of these cracks, but have a slatey frac- 

 ture parallel to the roof and pavement of the coal. 



With regard to the tons of coal of 20 cwt. each, con- 

 tained in an English or Scotch acre, the weight of a 

 cubic foot of coal varies from 75 to 80 pounds avoirdu- 

 pois, which gives a range in the cubic yard from 18 

 cwt. to very near a ton. In practice it is common to 

 reckon the cubic yard 18 cwt. which is exactly half a 

 hundred weight for each inch in height of the square 

 yard ; upon this principle a coal three feet four inches 

 in thickness contains a ton in every square yard of the 

 area, hence an English and Scotch acre of this thick- 

 ness contain the following weight of coals : 



Tons of 

 coal in an 

 acre. 



PLATI 



cccxci. 



An English acre 

 A Scotch acre 



Tons. 

 481-0 



608* 



From the above quantities, there falls to be deduct- 

 ed the proportion of coal to be left in pillars, besides 

 an allowance- for waste, before the exact produce per 

 acre can be ascertained ; from the above data, the quan- 

 tity of coal of any thickness contained in an acre, may 

 be very easily calculated, but the calculations must be 

 corrected according to the kind of coal and peculiari- 

 ties connected with it. 



When the engine-pit is sunk, and the lodgment 

 formed, the next thing to be done in collieries of a 

 moderate depth, and where a number of pits are to 

 be sunk for drawing the coals, is to run a mine in the 

 coal to the rise of the strata, or a cropping from the 

 engine-pit to the second pit. Where inflammable air 

 abounds, the primary point of attention is the venti- 

 lation for the safety of the workmen; but as this is 

 an intricate and important point in the mining opera- 

 tions, the opening up of a colliery will be described, 

 where only carbonic acid or fixed air is found ; where 

 there is little danger, and where the means of ventila- 

 tion are of the simplest kind. In many mining dis- 

 tricts, the second pit sunk to the rise of the engine- 

 pit, is named the bye-pit, that is, the pit farther up. 

 The mine which is carried from the engine-pit to the 

 second pit, may be 6' or 8 feet in width, and is either 

 carried in a line directly to the pit-bottom, or it is 

 carried at right angles to the backs or web of the coal, 

 until it is on a line with the pit where a mine is set off, 

 upon one side to the pit bottom. This mine is carried 

 parallel to the backs, or as nearly so as possible, till 

 the pit is gained. Fig. 5. Plate CCCXCI. repre- 

 sents this operation ; A the engine-pit, B the bye-pit 

 ' - or second pit, AC the mine run at right angles to the 

 backs, CB the mine set off to the left hand parallel to 

 the backs. Mines which are carried in this direction 

 at right angles to the backs, or parallel to them, are 

 the best, because the pillars which are formed next 

 them are in equal areas, stronger than pillars form- 

 ed by the sides of mines, which are driven oblique 

 to the backs and cutters, particularly if they are of an 

 l)io head 9P en kind. The next operation is to drive the dip- 

 levels. head or main-levels from the engine- pit bottom, or 



from the clip hand of the backset immediately adjoining Mines of 

 the engine-pit bottom ; for this work the best colliers 'oal. 

 are always chosen, as the object is to drive the mine """ "Y""" / 

 in a true level direction, and that independently of Workin 6 of 

 all sinkings or risings of the pavement. This mine is coa ' 

 generally not more than six feet wide in coals of or- 

 dinary thickness ; the rule is, to have upon the dip- 

 side of the mine, a small quantity of water, like that of 

 a gutter, so that it shall always be about four or six 

 inches deep at the forehead upon the dip-wall. In 

 coals which have a great dip, the water may be eight 

 inches deep ; and in very flat coals from two to three 

 inches will be sufficient; for this reason, that if the dip 

 io 1 in 3, then the water which is 8 inches deep will be 

 in breadth 24 inches, whereas in a coal dipping 1 in 

 12, the water 3 inches deep will be in breadth 3 

 feet. When the level is driven correctly with the spe- 

 cified depth of water, it is said to have dead water at 

 the forehead ; the miner, therefore, in this operation, 

 pays no regard to the backs or cutters of the coal, 

 but is guided in his line of direction, entirely by the 

 water, which he must alone attend to, and that with- 

 out regard to slips or dislocations of the strata which 

 may throw the coal up or down. In Fig. 5. the coal- PLATE 

 field is a portion of a bason, from which it is evident CCCKCI. 

 from what was before stated, that if the shape is uni- F 'S- 5 - 

 form and unbroken, and if any point is assumed a dip- 

 ping from the crop as D, the level lines from that point 

 will be parallel to the line of crop as DE, DF, and the 

 levels from any point whatever a dipping, will be also 

 parallel to these ; therefore, if the coal-field is an entire 

 elliptical bason, the dip-head levels carried from any 

 point would be elliptical, and parallel to the crop If, 

 however, and which is more commonly the case, the 

 coal-field is only a portion of a bason formed by a great 

 dislocation or slip of the strata, as represented in Fig. 



6, where a a a is the crop, and AB a slip of great mag- 

 nitude, forming another coal-field on the side C, then 

 the crop not only meets the cover, but is cut off by the 

 slip at A and at B. If, therefore, any point is assumed, 

 as D, for an engine-pit, the levels from it will proceed 

 in a line parallel to the crop, as D d, D c, and the level 

 on both sides of the engine pit will be cut oft' also by 

 the slip AB. In this Figure, the shaded part is the 

 breadth or breast of coal-field won by the engine-pit 

 D : what is not shaded is termed the under-dip coal, 

 and can only be wrought by one or more new winnings 

 towards the dip, according to circumstances Had the 

 engine-pit been placed at the point E, close to the slip 

 AB, it would have drained or won the whole of that 

 coal-field, and no level mines could be driven, but a 

 common mine run from E to B, and from E to A ; 

 which mines, in place of being level, would have a mo- 

 derate rise from E to B and from E to A, where they 

 would terminate with the coal where the crop meets 

 the cover. In such a case, these mines are not carried 

 close to the slip, but a few yards to the rise of it, in or- 

 der to leave a barrier or chain wall of coal to support 

 the superincumbent strata, which are ready to give 

 way at the fissure of the slip where all the strata are 

 disjoined and dislocated. 



The third general case as to dip-head levels, is when 

 the coal-field is a portion of an inverted bason, as Fig Kig. 7. 



7, where a a a is the crop of a coal, and B any point 

 assumed for an engine pit to make a winning. In this 

 case, the dip-head levels will proceed from B to c and 

 from B to b, parallel to the crop, till they are cut off 

 either by a slip AC, or reach a trough, where the coal 

 rises in different directions. In extensive coal-fields, 

 which are in general lying fair, if a conical swelling of 



