A. Stmhan — Explosive Slickensides. 403 



and drop out. The smooth sides lie face to face, and have the 

 appearance of being shot with a plane, consisting of various members. 

 There is generally two of these divisions in our forefield at Haycliff, 

 about eight or ten inches asunder, and a seam of white hebble^ in 

 the middle of that space, half an inch thick, in which the miners 

 rake down a sharp pointed pick until the crackling ceases ; then they 

 run away, knowing that the explosion will follow in a minute or two. 

 Sometimes a noise is heard like the beating of a church clock, after 

 which the greatest explosions happen. — I am, yours, etc., William 

 Mettam. — To Mr. George Tissington, Winster." 



John Mawe also writes in 1802 that in the Odin Mine "is found 

 that singular variety of lead ore, called sliclcenside. This galena 

 presents a smooth surface, as if plated. Sometimes it forms the sides 

 of cavities, and on being pierced with the miner's tool, rends with 

 violence, and explodes with a crackling noise. The cause of this 

 phenomenon has not been fully explained. I have seen a man, when 

 lie came out of the mine, only a few minutes after the explosion, 

 who, regardless of the danger, had pierced the sides of this substance, 

 and was much hurt, and cut violently, as if stabbed about the neck 

 ^nd other places with a chisel, whence he was unable to return to 

 the mines for two weeks." ^ 



" Sometimes the vein-stuff is found perfectly divided vertically, 

 throughout, and the surfaces polished ; and these are called Slichen- 

 sides or Cracking- whole, which usually are ribbed or slightly fluted, 

 horizontally : the appearances are very similar to those of faults, 

 but extraneous matters do not usually accompany them, the sides 

 being mostly in very close contact ; and often, after one side is 

 removed, so as to give room, especially if the surface be pecked or 

 broken, large Slapits, Spels, or fragments fly off, sometimes with 

 loud explosions, and continue so to do for some daj'S or longer, until 

 the gate or passage in such vein is greatly enlarged thereby : this is 

 the case in Gang Mine, in Cromford, where the hard 1st Toadstone 

 also, in the gates and shafts, thus spels off, until they want timbering 

 often, to support the roof and sides. I could not learn, that the 

 Slickensides in the Mines about Eyam explode now, on mere 

 scratching, as tliey were said to do in the late Mr. Whitehurst's time." " 



"In Gang Mine, where a Sliclcenside runs through the Vein, the 

 Miner avails himself of a curious property attending such Veins, by 

 drawing laces, stoops, or nicks, at about six inches apart and four 

 inches deep, with the point of his Pick, from top to bottom of his 

 face of work, when he then leaves for several hours, and on his 

 return, finds all the Vein-stuff so furrowed, spelled, or slappeted off, 

 and laying on the sole ready got to his hands." ^ 



"When their edges occur in the face of the vein, on the miner 

 striking his pick into the vein they separate, in some districts without, 



^ Kebhle, a -white opaque spar, calcareous, but not apt to break into rbomboidal 

 lorms. 



2 Tbe Mineralogy of Derbysbii-e, by John Mawe, 8vo. London, 1802, p. 48. 



3 General View of tbe Agriculture and Minerals of Derbvsbire, by Jobn Farey, 

 8vo. London, 1811, vol. i. p. 250. ^' lb. p. 367. 



