Mr Bald o7i tJie Fires that take place in Collieries. 105 



ried on by one pit. This regular and scientific mode is repre- 

 sented by the diagram, fig. 1. Plate II. 



When a pit is sunk to the coals, mines, termed Headways, 

 are run from both sides of the pit, in a level course direction as 

 a main road a, a, for bringing the coals from the miners to the 

 l)ottom of the pit, and at regular distances, according to the 

 system pursued by the mining engineer who directs the colliery 

 operations ; openings are made in the coal, next to the pave- 

 ment, or rock, on which the coal-bed rests, which openings are 

 about eight feet wide, and seven feet high : these are termed 

 bolt-holes, and are marked b ; from these bolt-holes the working 

 of the coal is extended, and by these the excavations, marked c, 

 are made of from two to three hundred feet in width and 

 breadth, and there is left around each excavation a strong bar- 

 rier of coal, as represented in the figure, to insulate the excava- 

 tion. 



As much small-coal rubbish, mixed with pyrites, is left within 

 the excavated area, if the free access of air were permitted 

 thereto, spontaneous ignition would soon take place ; but this is 

 commonly effectually prevented by placing a stopping, as it is 

 termed, in the bolt-hole. At first this was done by stones 

 and common rubbish, but this was in many instances found to 

 be ineffectual, and the most secure method is proved to be, by 

 building two walls across the bolt-hole, composed of loose stones, 

 at some distance from each other, and filling up the space be- 

 twixt them with mine dust, that is, with the dust of calcined 

 ironstone, produced at iron works. This, aided by the mois- 

 ture of the mines, becomes a solid mass, quite impervious to 

 air, and is not injured by the crushing of the strata, as is the 

 case with stone walls, which are crushed into a loose powder, 

 through which air will pass. By this simple method, sponta- 

 neous ignition is now generally prevented in the Dudley district. 



In the north of England collieries, namely, those on the 

 rivers Tyne and Wear districts, where the coal occasionally 

 takes fire, the danger is exceedingly increased by the presence 

 of hydrogen gas, which sometimes accumulates, then fires and 

 explodes at the burning mass ; accumulates again, and goes off 

 at regular intervals, loud as the thunder of heaven, when the 

 bright blaze of conflagration is succeeded by a darkness so 



