1867.] The Ventilation of Coal Mines. 187 



of the workings, and allowing the roof to fall in : this forms a 

 waste, commonly called the " goaf" or " gob."* 



The " long-wall " mode of working consists in carrying pas- 

 sages to the extremity of the property, and then working away 

 the coal in one long face, supporting the roof by props for a time, 

 and eventually, by walls formed of stone from the mine. 



A word or two on mining appears necessary. The order of 

 the operation is this : — The coal is cut and got by " hewers f 

 it is then moved in the tubs through the first passages by 

 "putters;" horses draw several of these tubs to the shaft-foot, 

 and these are drawn to the surface by the steam-engine. Only 

 one of these processes — the hewers' — has any direct effect on the 

 liberation of gas, but they all have an important bearing on 

 the plan of the underground roads and methods of ventilation. 

 The roof which overlies the cavities made in removing the coal by 

 the hewers may have a tendency to fall in, and pour inflammable 

 gas into the " roadways " or " air channels." The " thill " or floor 

 may, being relieved from the pressure of the superincumbent masses, 

 be subject to heave and discharge gas upwards ; there may be in 

 front of the workings, especially along lines of dislocation, undis- 

 covered reservoirs of such gas: it may have accumulated in the 

 broken ground or "goaf" (which has been described), which, once 

 abandoned, is rarely ever explored again. All these may be 

 regarded as sources from which gas may flow, and, under a judi- 

 cious system of working, they should be carefully guarded against. 

 The main source, however, of inflammable gas, and that which 

 yields by far the greater, but not the most dangerous, supplies, is 

 the cutting of the fresh coal in the ordinary process of every-day 

 work. " It will be observed," says one of the inspectors, " that 

 about three-fourths of the explosions take place in stagnant places in 

 1 winning forward ' new drifts, where the openings were in course 

 of being made, and the ventilation not brought close up to the face." 

 This will satisfactorily show that the coal is in its natural condition 

 constantly evolving gas, and that the admission of atmospheric air 

 has nothing to do with the liberation of the fire-damp gas. 



Coal is cut by the " hewers " in two directions, at right angles 

 to each other ; these are called " boardways " and "headways." 



It is found as a matter of experience, that in driving " board- 

 ways course" whatever gas exists in the coal comes off more 

 freely from the numerous fissures which are cut across. In most 

 seams of coal a definite structure is observable, innumerable small 

 fissures are found to run in a uniform direction, or nearly so ; this 



* Goaf is equivalent to the Gob of the Midland Counties*, and the " Vugh," 

 or " Vugha," of the Cornish miners. It is probably of Cymric origin — from 

 " Ogof," a cave or hollow. The Gogofau, or Ogofau, is the name of a Roman 

 gold-mine near Pumpsant, in Caermarthenshire. 



