152 COMMON COAL. 
haven. The particular places whence they are obtain- 
ed have the name of collieries, and the mines from which 
they are dug are called pits. The deepest of these are 
in Northumberland, and are worked at more than 900 
feet below the surface of the earth. At Newcastle there 
is a coal-pit near 800 feet in depth, and which, at that 
depth, is wrought five miles horizontally, quite across, 
and beneath the bed of the river Tyne, and under the 
adjacent part of the county of Durham. At Whiteha- 
ven the mines are of great depth, and are extended 
even under the sea, to places where there is above them 
sufficient depth of water for ships of great burthen, 
and in which the miners are able sometimes to hear 
the roaring of the water. On the contrary, in some 
parts of Durham the coal lies so near the surface of the 
earth that the wheels of carriages lay it open, and in 
such quantity as to be sufficient for the use of the neigh- 
bourhood, r- 
The beds of coal are of various thicknesses, from a 
few inches to -several feet; and in some places, it is 
found advantageous to work them at a very great depth, 
although their thickness does not exceed four or five 
feet. The thickest bed of English coal, of any extent, 
is that of the main coal in Staffordshire, which measures 
about thirty feet. In many places there are several 
beds above, and parallel to, each other, separated by 
strata of slate, sandstone,, and other minerals. Coal is 
never found in chalk, and very rarely in limestone. 
At Whitehaven, the principal entrance to the coal- 
mine, both for men and horses, is by an opening at the 
bottom of a hill, through a long passage hewn in a rock. 
This, by a steep descent, leads to the lowest bed of 
coal. The greatest part of the descent is through 
spacious galleries, which intersect other galleries; 
all the coal having been cut away, except large pil- 
lars, which, in deep parts of the mine, are three yards 
high, and about twelve yards square at the base, such 
great strength being there required to support the pon- 
derous roof. There are three distinct and parallel strata 
