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about fifteen miles over every way. Frequently, Mr. Williams ob- 
serves, tbe seams of coal rise up to day, and then seem to decline 
a little way down from the surface of the earth to a sufficient depth 
to be preserved fresh and good, even in full perfection, until the 
exigencies of society have occasion for them ; and that, when they 
have declined so far, they then become quite flat, and afterwards 
rise again upon the opposite side of the coal field, with an opposite 
dip and rise, and so form a great trough, resembling a valley ; 
which is, he remarks, one of the best similitudes of this position of 
the seams of coal in a coal field that can be imagined. 
Yours, &c. 
LETTER XVII. 
PARTICULARITIES OBSERVABLE IN DIFFERENT COAL-PITS 
CANNEL COAL PYRITES, ETC. 
Having thus endeavoured to furnish you with a compendious 
account of the particular circumstances which accompany the dis- 
position of coal, I shall, for the sake of supplying a few more pmnts 
of comparison, lay before you a sketch of some of the more inte- 
resting mines of coal ; that you may be the better enabled to detei - 
mine how far the attempt which I shall make, to account for their 
existence, agrees with the phenomena which nature presents to oui 
observation. 
At Bishop-Sutton, near Stowey, in Somersetshire, the first solid 
vein is called the stinking vein, from its peculiar impregnation 
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