334 



MINE. 



Mines of 

 



coal-field. 



1'nTE 

 CCCXC. 



Fig. 7. 



Quick- 

 sands in 

 day levels; 



Fig. 8. 



cessary to sink an air pit upon the level, by which a 

 strong circulation of air is not only produced, but the 

 m ' ne st "ff ' s more easily drawn up than taken out to 

 the mouth of the mine. Formerly these air pits were 

 sunk directly upon the level, but that mode is now 

 given up; for this reason, that if any part of the sides 

 of the pit gave way, the rubbish instantly choked up 

 the level, and frequently occasioned much trouble and 

 expence to get it cleared again. The practice now is, to 

 sink these pits about eight or ten yards from the side of 

 the level, and connect them by a side mine. In this 

 manner, day-levels are carried forward for miles, and 

 may be carried to any distance. If, in the progress of 

 the level, workable coals are intersected before reach. 

 ing the coal which is the main object of the mining 

 adventure, an air pit may be sunk of such dimen- 

 sion as to be suitable for a coal-pit, by which coals may 

 be drawn. Air pits generally do not exceed seven feet 

 diameter ; and they ought always to be of the form 

 of a circle. Plate CCCXC. Fig. 7, represents a coal- 

 field, where the fitting is made by a day-level ; a is the 

 mouth of the level at the surface of the sea, b, c, d, c, are 

 coals intersected, and drained by the level. All the 

 coals lower than the level can only be drained by ma- 

 chinery. A, is a coal-pit sunk upon the coal c ; if the 

 level is carried forward, the coals f, g, and any other 

 coals which lie in that direction will also be drained, 

 and may be wrought by means of the pit A. The ef- 

 fect of the level would be the same if the coals and stra- 

 ta had dipped in an opposite direction to that represent- 

 ed in the figure. 



The chief difficulty or obstacle which has occurred in 

 executing day levels, is thick beds of quicksand which 

 are found in the alluvial cover. Instances have been 

 found in practice where ingenuity, determination, and 

 resolute perseverance, could not command success ; for 

 although thick beds of quicksand can now be passed 

 through in a perpendicular direction, by adopting 

 approved of plans, the difficulty of passing through 

 them in a horizontal line has not yet been surmount- 

 ed. If such a sand-bed is found to obstruct the drij- 

 ing of a day-level; and if it is an object to carry for- 

 ward the level from that particular point, the mode of 

 proceeding is as follows. Fig. 8. represents the strata 

 of a coal-field A, with the alluvial cover a, b, containing 

 the bed of quick-sand b. B is the lower part from which 

 the level is required to be carried in the direction B, d. 

 But the quick- sand renders this mode of operation im- 

 practicable. The pit B C is sunk through the quick- 

 sand by means of tubbing, as will be described when 

 treating of pit-sinking ; and when the pit has been sunk 

 a few yards into the rock, the level mine or drift is car- 

 ried forward to the point D, when the pit E D is put 

 tlown, it having been previously ascertained, by boring 

 through the alluvial cover, that the rock-head at F is 

 a few yards higher than the mouth of the pit B. Dur- 

 ing this operation all the water and mine stuff are drawn 

 at the pit B ; but the instant the pit ED communicates 

 with the mine, the water is allowed to fill the mine CD, 

 and grow up both pits until it finds an issue at the mouth 

 of the pit B. From the surface of the water at G, in 

 the pit ED, a mine is begun of the common dimensions, 

 and carried forward until the coal in search of i inter- 

 sected. By this plan no level is lost. This kind of 

 level is named a drowned level, a blind level, and also 

 an inverted syphon. When a coal, or any number of 

 coals, are intersected by a day-level, the operation of 

 working the coal proceeds in the usual manner, as will be 

 described when treating of the manner of working coal. 



In carrying forward levels into a coal-field of such 

 dimensions, as to be used as a canal, the same general 

 rules are observed as in driving a common-level, the 

 only difference being in the dimensions ; but, from the 

 width being great, a greater proportion of the sides and 

 roof requires to be built and arched for security, which 

 greatly adds to the expence of the operation. When 

 such under-ground canals or levels extend to a great 

 distance, they can be easily ventilated without air- 

 pits, on account of their width ; or, if ventilation is 

 necessary, it is accomplished either by air-pipes, or by 

 wide bore-holes put down from the surface ; so that if 

 air-pits are found necessary, they are placed at a great 

 distance from each other, and as the stuff produced 

 in driving the mine is in great quantity, it is brought to 

 the mouth of the mine by canal-boats ; but rail-roads 

 must be used at the forehead. This part of the operation 

 is not commenced until the level has advanced about 

 half-a-mile under cover. This mode of proceeding is 

 represented Fig. 8. Plate CCCXC IV. where A is the 

 canal which enters under cover at B, the stuff from 

 which is taken out by means of rail-roads as far as the 

 point C ; at this place a step is left a few inches higher 

 than the deptli of the water, and the canal is filled. 

 From the level of this step the mine is carried forward 

 to the forehead D, and all the stuff produced is brought 

 in carriages along a rail-road, and emptied into the boats 

 at C. When this operation has advanced to a conveni- 

 ent distance, the rail-roads are lifted, and the step at C 

 is formed with a platform C, a, having an inclined plane 

 formed of the rock a, b, which reaches to the bottom of 

 the mine. The sole is then carried forward in a true 

 water level line in the direction b, c, until it is as far ad- 

 vanced as the forehead D. The stuff produced by this 

 last part of the operation is carried along rail-roads ; 

 and the loaded carriages are drawn up the inclined 

 plane a, b, by means of a jack-roll, or windlass, placed 

 at a, where they are emptied into the boats at C. The 

 next operation is to remove or cut out the step or bench 

 of rock left at C. For which purpose, a temporary 

 dam- head, made of deals, is placed across the canal at C, 

 as high as the water, having clay at die back to prevent 

 leakage ; the step a, C, is then cut out as low as the bot- 

 tom of the canal, and upon removing the temporary 

 dam, the water fills the canal to the forehead D, to which 

 point the boats navigate ; and the same operation goes 

 on successively to any required distance, viz. until all 

 the coals or other minerals of the district, proposed to 

 be laid dry, and wrought by the mine or level, are in- 

 tersected. 



When a coal-field iS so situated as not to be rendered 

 level free, the winning has to be made by means of ma- 

 chinery. 



In the early periods of mining, the drawing of water 

 from the mines was most laborious, when either men or 

 horses had to be employed ; and when this was the case, 

 the mining operations were very limited both as to depth 

 and extent below ground. The chain and bucket 

 engine was the most powerful of the machinery then 

 employed, and when wrought with a water wheel, rais- 

 ed a great quantity of water ; but the greatest depth to 

 which it was applied, was from 40 to 50 fathoms. The 

 machines or engines presently in use for the drainage 

 of coal-mines are, 



lit, The hydraulic engine, or water wheel, with 

 cranks and vibrating beams. 



Zd, The common atmospheric steam-engine, invent- 

 ed by Newcomen, known by the name of Newcomen's 

 engine. 



Mines of 

 Coal. 



Winning i 

 coal-field. 



Day level 

 used as a 

 canal. 



PLATS 

 CCCXCIV. 



Fig. 8. 



Winning i 

 coal-field 

 by machi- 

 nery. 



