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from ignited pyrites, are frequently difcovered in the 
bottom of mines and coal-pits ; and are often detri- 
mental, and fometimes deftruCtive, to the miners; 
which made the late learned Dr. Woodward, and 
others, imagine, that they were vapours ariflng from 
an abyfs. 
From what has been faid therefore, we may, in my 
humble opinion, draw the following conclufions. 
1. That all fubterraneous fires, even thofe of 
Hecla, Vefuvius, and ./Etna, together with thofe ob- 
ferved in the mines and coal-pits, are caufed by the 
heat and fixing of pyrites and marcafites. 
2. That the waters of our hot baths derive their 
heat from pafling over a bed of ignited pyrites. In- 
deed the folid contents of thofe waters do evidently 
prove this affertion being nothing more than fuch par- 
ticles of the pyrites as are foluble in water. 
z. That thefe mineral flames will be more or 
lefs fubtil, according to the minutenefs of the par- 
ticles of the combuftible matter, and the quantity of. 
phlogiflon, which they contain. 
4. That the convulflve motions and tremblings 
of the earth are caufed by the heat of the burning 
pyrites expanding the air contained in its bowels. This 
is clearly proved, by their cauflng, immediately after, 
an eruption of the earth, which generally difcharges 
a dark coloured cinder-like and frothy matter. And, 
5. That thofe places, where the earth contains 
the greateft quantity of pyrites and marcafites, will 
be mofl liable to thefe convulflve motions and trem- 
blings, no other natural caufe contradictory. 
However, I fball, with great refpeCt, fubmit thefe 
obfervations to the confideration of the Prefident and 
Fellows. 
