Clifton College Scientific Society. 61 



■way of sinking pits or vertical shafts ; the other, driving levels or 

 lateral shafts in the sides of the hills. Of course, the latter mode 

 can only be practised with success where there are high hills, and 

 where the coal-seams lie above the level of the valley, but it is a 

 system very generally practised in South Wales. The deepest pit 

 or vertical shaft in the field is one sunk in the Ffochrhiw Colliery 

 (by the Dowlais Company), which is 1305 feet deep. 



The coal-field contains good fireclay, alum-shales, and horn- 

 coal, yielding at Pontypool fifty to fifty-five gallons of crude oil 

 per ton of shale. By removing in distillation twelve to fifteen per 

 cent, of mineral turpentine (used generally for machinery, paint, 

 and out-door ironwork) a good lubricating oil is left, and from it, 

 by further refining, fine oil is produced. It also contains paraffine. 



The first mention of coal being worked in this field we find to 

 be about the year 1570, in a description by George Owen, Esq., 

 of Henllys, Pembrokeshire. In 1697, nearly a hundred years 

 later, the first fossil from the coal — a Stigmaria — was described 

 by Dr Tancred Eobinson of Usk, Monmouthshire. The steam 

 coal was first worked in 1836 by Messrs Wayne, near Aberdare. 

 The coal raised in this field in 1854 was 8,500,000 tons, in 1868, 

 13,210,000 tons; being an increase of 4,710,000 tons in fourteen 

 years. 



The pig-iron made in this district in 1827 was 272,000 tons, 

 and, in 1868, 894,255 tons, being an increase of 622,2.55 tons in 

 forty-one years. The highest ground in the coal-field is Garn- 

 fach, south of Hirwain (1971 feet), but just beyond the northern 

 outcrop the old red sandstone, composing the Brecknockshire 

 Beacons, rises nearly to the height of 3000 feet. 



There are two ways of working the coal after the pit has been 

 suuk or the level driven. One is called ' post-and-stall,' the other 

 the 'long-wall' system. The post-and-stall or board-and-pillar 

 system is the one most largely practised : the men open ranges of 

 working places, each as wide as the nature of the fioor and roof 

 will admit of with safety, and each divided from its neighbour by 

 masses of coal broad enough to sustain the pressure from above. 

 The long-wall system is directly opposite to this. In working 

 upon this method the men remove the whole breadth of coal over 

 a long continuous face, supporting the roof at the immediate 'face' 

 or end of the workings by temporary props, and allowing the 

 superincumbent strata to break down bodily at a few feet distance 

 behind the workmen. 



It will be as well to explain here some of the most familiar 

 mining expressions. In the case of a vertical shaft, as soon as the 

 coal is reached, the men proceed to drive a level — that is, they 

 cut a passage, horizontal or nearly so, but sloping slightly towards 



