402 A. Strahan — Explosive 8lickensides. 



laid on, as if only rubbed over with black lead, tbougli sometimes 

 thicker. 



" 6. The vein in Haycliff Mine contains two of the above seams, 

 and therefore may be compared to three slabs of marble, the middle 

 one polished on both sides and in contact with the other two. 



" Thus are the above veins circumstanced. Now what is yet more 

 remarkable is this : if a sharp pointed pick is drawn down the vein 

 with a small degree of force, the minerals begin to crackle, as sulphur 

 excited to become electrical by rubbing ; after this in the space of 

 two or three minutes, the solid mass of the minerals explodes with 

 much violence, and the fragments fly out, as if blasted with gun- 

 powder. These effects have frequently happened, by which many 

 workmen have been wounded, but none killed, both in the Eyam 

 Mines, and in that called Oden, at Castleton. 



" In the year 1738 a prodigious explosion happened in the mine 

 called Haycliff. The quantity of two hundred barrels of the above 

 minerals were blown out at one blast ; each barrel, I presume, con- 

 tained no less than three or four hundredweight. At the same time 

 a man was blown twelve fathoms perpendicular, and lodged upon a 

 floor, or bunding, as the miners call it, in one of the shafts. 



" When the above explosion happened, the barrel, or tub, in which 

 the minerals, etc., are raised to the surface, happened to hang over 

 the engine shaft, which is nearly seven feet in diameter, and 448 

 yards distant from the forefield, or part, where the explosion happened ; 

 this barrel, though of considerable weight, was lifted up in the hook 

 on which it was suspended ; and the people on the surface felt the 

 ground shake, as by an earthquake. 



" Such are the effects which have frequently been produced in all 

 the above mines ; but from what cause they proceed, 1 have not yet 

 been able to discover, nor even the least traces towards it. The 

 substance having been analized, is found to consist of fluor and the 

 ore of lead, but the cause of explosion still remains equally mysterious, 

 though some attempts have been made to obtain a knowledge of this 

 curious phenomenon. 



"These curious observations I received from Mr. Mettam, of Eyam, 

 overseer of the mines, who also addressed the following account of 

 them to Mr. George Tissington, of Winster, principal agent of the 

 works. 



" Eyam, 2 July, 1768. Sir, — I send you by the bearer, two speci- 

 mens of our slickensides, containing all the variety of minerals 

 where the explosions happen ; they fly out in such slappits,^ smooth 

 on one side. The explosions are sometimes heard to the surface, and 

 felt like an earthquake ; they frequently blow out all the candles in 

 the mine, and split the stemples ^ into splinters as small as the twigs 

 of a birch besom, to the distance of thirty or forty yards from the 

 forefield ; ^ others are broke, and some of them become too short 



^ Slappits, fragments of the minerals burst out of the yein. 



"^ Slemples, joists laid across fissures, when the minerals are cut out, by way of 

 making a floor, on which rubbish is deposited, to save the expense of raising it to the 

 surface. ^ Forefield, that part of the vein under workmanship. 



