COAL, 
4 6o 
of the globe penetrated to so great a depth below 
the surface of the sea; the very deep mines in Hun- 
gary, Peru, and elsewhere, being situated in moun- 
tainous countries, where the surface of the earth is 
elevated to a great height above the level of the 
ocean. 
t£ There are here three strata of coal, which lie 
at a considerable distance, one above another ; the 
communication between each is preserved by pits. 
The vein is not always regularly continued in the 
same inclined plane, but is sometimes interrupted 
by hard rock ; and in those places the earth seems 
to have sunk downwards from the surface, while the 
part adjoining hath retained its antient situation. 
These breaks the miners call dykes', and when they 
meet with one of them, they first observe whether 
the direction of the strata is higher or lower than in 
the part where they have been working. If, to 
employ their own terms, it is cast down , they sink 
a pit to it with little trouble ; but should it, on the 
contrary, be cast up to any considerable height, they 
are frequently obliged to carry a long level through 
the rock with much expense and difficulty, till they 
again arrive at the vein of coal. 
“ In these deep and extensive works, the greatest 
care is requisite to keep them continually ventilated 
with perpetual currents of fresh air, to expel the 
damps and other noxious exhalations, and supply 
the miners with a sufficiency of that vital fluid. In 
the deserted works, large quantities of these damps 
are frequently collected, and often remain for a long 
2 H 
VOL. III. 
