264 Of the Principles 



ferent fort, according to circumftances, rmy be 

 produced from the damps arifing from this ore. 



(2.y As in the bowels of the earth, quite other 

 caufes and circumftances may concur, by which all 

 ores, and fuch as we find unaffected at the day, may 

 become fubjed to weathering. 



Now the four, hinted at above, are alum- ore, 

 cobald, bifmuth-ore and pyrites,. Cobald, when 

 expofed long in the heap, either in a dole, damp, 

 moilt room, or to the open air 9 rain and iun ? efpe- 

 cially in fmall pieces, or a meal, becomes fo heated, 

 as to emit a (harp, fweetifh damp or vapour from it. 

 Hither alfo bifmuth-ore is referable, which not only 

 generally adheres, but is alfo nearly allied to fmalt- 

 cobald, and ufually bewrays its weathering among 

 cobald, with an efflorefcence of -a peach-bloom co- 

 lour. Alum-ore, particularly the fort of a woody 

 original, and ftill containing woody matters among 

 it, and of a bituminous nature and quality, as the 

 large alum-mine at Commodau in Bohemia, which 

 takes fire in the air, after lying a little expofed on a 

 heap in the weather and fun ; fo as not only vio- 

 lently to fume, but alfo turn to a coal, and burft out 

 into actual flame ; for which reafon it muft be often 

 dafhed with water, Stone-coal, fo far as it is ge- 

 nuine, and not conftfting in bituminous, light, alu- 

 minous matters, has not, fo far as I know, the fame 

 effect as this alum-ore. And the queftion is, whe- 

 ther fuch accenfions in coal-pits are fpontaneous, or 

 heedlefsly caufed from actual flame and fire. 



Limeftone appears, as was hinted above, even in 

 its unburnt ftate, to be fitted for weathering, and to 

 bear fomething to be extracted from it, communi- 

 cable, if not to the air in form of a damp, or va- 

 pour, 





