286 
Mr. Weaver on the 
These troughs, or basins, are generally from fifty to seventy yards 
deep from the surface to the bottom of the channel of the upper bed of 
coal ; the middle of the channel being flat, while the sides gradually 
acquire a higher angle of elevation toward the outcrop of the coal. 
The breadth of these troughs is usually 500, 600, or 700 yards, at 
the surface. 
§ 186. The structure, here described, may be clearly traced by 
crossing the country from Littlefield on the north-west toward 
Lismullin on the south-east, passing through the coal field of Mr. 
Langley of Coalbrook, and leaving Ballingarry on the east. It is 
the line represented in the section of this district ; (see Plate 14. 
No. 4.) 
We thus traverse a succession of coal troughs, bearing the names of 
the Five Mile Seam, Knockbrack, Coalbrook, Canal, Clashdufife, and 
Copper or Raygrass troughs. All of these, except the first, are 
found on Mr. Langley’s estate of Lisnamrock, but they extend into 
adjoining properties in a north-east and south-west direction, with 
the exception of Knockbrack and Copper troughs, which extend 
from Mr. Langley’s property, only toward the south-west. 
The north-western outcrop of the Five Mile seam is within a 
quarter of a mile of the declivity on that side ; and the south- 
eastern outcrop is about 600 yards distant. On either side the seat 
grit rock may be traced rising up to the surface ; but in proceeding 
across the country to the south-east, this rock may be observed 
gradually forming arches between the several troughs, which are 
either entire and flat at the top of the arch, or sometimes broken, 
presenting interrupted strata with opposite dips. The beds which 
surmount the seat rock are sometimes broken in a similar man- 
ner; and these fractures afford in one instance an opportunity 
of observing a repetition of the series. Thus, in the broken arch 
