Geological Relations of the East of Ireland , 289 
out- crops on the south been traced ; but the question of their con- 
tinuity might be set at rest by judicious borings, conducted to ade- 
quate depths. 
§ 191. The Five mile seam varies from fifteen to eighteen inches 
in thickness. It has been wrought for culm by a long line of pits, 
particularly along the northern outcrop, but without system. 
The Lisnamrock seams are generally from 21 to 27 inches thick, 
average two feet. The Coalbrook seam, on which the present 
workings are conducted, yields, from every breast-work of 20 square 
yards of the seam, three tons of merchantable coal, and from three to 
three and a half tons of culm, or about 2352 tons of coal and culm per 
Irish acre. These collieries are well circumstanced in regard to the 
roof, which is compact and firm ; and hence the coal is cut out clean 
in the broad way, and no pillars are left. As the workmen proceed, 
rough dry pillars of gritstone are inserted from time to time, and 
between these are stowed away that portion of the fire clay which is 
-cleared from under the coal, and part of the roof shale which is cut 
into, in forming the road ways. Hence, whenever the roof settles, 
it is in large sheets, not partially. The breast- works are always kept 
clear, and there is no difficulty in ventilation. The coal sells at the 
pit-mouth for twenty shillings per ton, and the culm for four shillings 
per barrel of twelve hundred weight, or 6s. 8d. per ton ; one half of 
which price is usually paid to the collier for raising and delivering 
the coal and culm on the bank, the miner himself bearing the cost of 
underground stores, hire of labourers, drawing of the coal, &c. 
The expense of machinery, agency, sinking of pits, &c. falls of course 
on the proprietor. 
§ 192. The general character of the grit rocks, or sandstone of 
this district, is that of a remarkably close and fine grained compound, 
hard and firm, consisting of minute grains of quartz with scarcely 
Vol. V. 2 o 
