173 



about fifteen miles over every way. Frequently, Mr. Williams ob- 

 serves, the 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, &C. 



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 points 

 of comparison, lay before yon- a sketch of some of the more inte- 

 resting mines of coal; that you may be the better enabled to deter- 

 mine how far the attempt which I shall make, to account for their 

 existence, agrees with the phenomena which nature presents to our 

 observation. 



At Bishop-Sutton, near Stowey, in Somersetshire, the first solid 

 vein is called the stinking vein, from its peculiar impregnation 



