22 



A HISTORY OF 



CHAPTER VIII. 



OF MINES, DAMPS, AND MINERAL VAPOURS. 



THE caverns, which we have been de- 

 scribing, generally carry us but a very little 

 way below the surface of the earth. Two 

 hundred feet, at the utmost, is as much as the 

 lowest of them is found to sink. The perpen- 

 dicular fissures run much deeper; but few 

 persons have been bold enough to venture 

 down to their deepest recesses; and some 

 few who have tried, have been able to bring 

 back no tidings of the place, for unfortunately 

 they left their lives below. The excavations 

 of art have conducted us much farther into 

 the bowels of the globe. Some mines in 

 Hungary are known to be a thousand yards 

 perpendicular downwards ; and I have been 

 informed, by good authority, of a coal-mine in 

 the north of England, an hundred yards deeper 

 still. 



It is beside our present purpose to inquire 

 into the peculiar contrivance and construction 

 of these, which more properly belongs to the 

 history of fossils. It will be sufficient to ob- 

 serve in this place, that as we descend into the 

 mint v s, the various layers of earth are seen as 

 we have already described them; and in some 

 of these are always found the metals or mine- 

 rals for which the mine has been dug. Thus 

 frequently gold is found dispersed and mixed 

 with clay and gravel;" sometimes it is mingled 

 with other metallic bodies, stones, or bitu- 

 mens ; h and sometimes united with that most 

 obstinate of all substances, platina, from which 

 scarce any art can separate it. Silver is 

 sometimes found quite pure ; c sometimes 

 mixed with other substances and minerals. 

 Copper is found in beds mixed with various 

 substances, marbles, sulphurs, and pyrites. 

 Tin, the ore of which is heavier than that of 

 any other metal, is generally found mixed with 

 every kind of matter : lead is also equally 

 common ; and iron we well know can be ex- 

 tracted from all the substances upon earth. 



a Ulloa. vol. ii. p. 470. b Ulloa, ibid. 



c Macquer's Chymistry, vol. i. p. 316. 



The variety of substances which are thus 

 found in the bowels of the earth, in their 

 native state, have a very different appearance 

 from what they are afterwards taught to as- 

 sume by human industry. The richest me- 

 tals are very often less glittering and splendid 

 than the most useless marcasites; and the 

 basest ores are generally the most beautiful 

 to the eye. 



This variety of substances, which compose 

 the internal parts of our globe, is productive 

 of equal varieties, both above and below its 

 surface. The combination of the different 

 minerals with each other, the heats which 

 arise from their mixture, the vapours they 

 diffuse, the fires which they generate, or the 

 colds which they sometimes produce, are all 

 either noxious or salutary to man ; so that in 

 this great elaboratory of nature, a thousand 

 benefits and calamities are forging, of which 

 we are wholly unconscious ; and it is happy 

 for us that we are so. 



Upon our descent into mines of consider- 

 able depth, the cold seems to increase from 

 the mouth as we descend ; e but after passing 

 very low down, we begin by degrees to come 

 into a warmer air, which sensibly grows hot- 

 ter as we go deeper, till, at last, the labourers 

 can scarcely bear any covering as they con- 

 tinue working. 



This difference in the air was supposed by 

 Boyle to proceed from magazines of fire that 

 lay nearer the centre, and that diffused their 

 heat to the adjacent regions. But we now 

 know that it may be ascribed to more obvious 

 causes. In some mines, the composition ot 

 the earth all around is of such a nature, that, 

 upon the admission of water or air, it fre- 

 quently becomes hot, and often bursts out 

 into eruptions. Besides this, as the external 

 air cannot readily reach the bottom, or be 

 renewed there, an observable heat is per- 



d Hill's Fossils, p. 628. 

 e Boyle, vol. iii. p. 232. 





