700 



GEOLOGY. 



Seam dipping. 



outlay of capital incom- 



patible with a profitable 



return. The labourer 



has to work in these narrow seams 



either on his knees, or in a less 



erect position, his helpers drawing 



the skiffs of coal cut away upon 



all- fours. When the seam dips 



at a considerable angle, the coal is 



drawn up the incline to a level by 



means of a windlass, as represented. 



Every pit which has been worked any length of time contains a number of these 



excavated seams, one above another, connected by trap stairs, all lying below the 

 bottom of the shaft of the mine, to which the coal has to 

 be carried. The height ascended, with the length of the 

 lateral passages, is often a journey equal to the ascent of 

 St. Paul's, but far more laborious, owing to the burdens borne 

 by the coal-bearers. Sometimes the subterranean highways, 

 instead of being connected by a trap staircase, are severally 

 reached by a " turnpike stair," a gradually ascending, spiral, 

 unrailed road. Besides the exhausting nature and the dreary 

 scene of their toils plying with blackened arms the pick- 

 axe, a hundred fathoms deep below the surface of the soil, in 

 damp and darkness which a few flickering lamps serve but 

 to render visible peculiar dangers threaten habitually the 

 mining population, from the /possibility of the roof of their 

 Subterranean workshop falling in upon them, or the explosion 

 of the inflammable gas evolved from the coal, through contact 

 with an unguarded flame. 



In no part of the world are the coal measures, with the 

 other members of the carboniferous system, so extensively 

 developed, within the same area, as in the British islands. 

 Leaving out of sight the great beds in the lowlands of Scot- 



land, and m Ireland, there are in England and Wales the following fields, the arrange- 



ment of which is adopted from Conybeare and Phillips ; 



COAL DISTRICT NORTH OF THE TRENT, OR GRAND PENINE CHAIN. 



1. Field of Northumberland and Durham, stretching from the river Coquet on the north 

 twenty four ^ 



f fift ^ ei S llt miles > bv a breadth > <* the greatest, of 



