A. Strahan — Explosive Siickensides. 401 



or slabs. Such sheets, when bared in the mining operations, fly 

 to fragments with explosive violence on being struck, or even 

 scratched by a miner's pick. The following extracts from old 

 authors, and from communications on the subject that I have 

 received, will serve to illustrate the nature of the explosions and the 

 manner in which the danger was met by the men. The accounts 

 relate chiefly to the mines near Eyam, but explosions occuri'ed also 

 in the Odin Mine near Castleton. 



The earliest reference to the subject wliich I have met with is by 

 Dr. Short :— 



" On the North Side of this Mountain [Hucklow Edge, near 

 Eyam] ... is a Mine which cannot be wrought ; for in picking 

 or striking the Ore, the sudden shaking of the Metal gives such a 

 violent Motion to the Sulphur, that it makes an Explosion like fired 

 Gunpowder, or a Blast in a Rock, so as great Lumps rise up and fly 

 about along with a Kind of Terrce Motus, or Earthquake." ^ 



Pilkington,^ writing fifty years later, remarks that " the crackling 

 and explosions caused by scraping these siickensides with a pick-axe 

 are well known, but hitherto not satisfactorily accounted for. They 

 are said to lose the above property very soon after they are taken 

 out of the mine. In regard to their external appearance, their 

 smooth side greatly resembles black lead very thinly spread over 

 the surface of any smooth body. But the rough side looks very 

 much like to common limestone." 



But the most detailed account is furnished by John Whitehurst,^ 

 and is, I think, of sufficient interest to be reproduced here in full : — 



" I purpose giving some account of an extraordinary phenomenon 

 which has frequently happened in Hay cliff and Lady wash Mines at 

 Eyam, and in Oden Mine at Castleton : the former are thus circum- 

 stanced. 



"1. The minerals are contained in the fissures of the limestone, 

 covered by a stratum of shale and grit, which retain their full thick- 

 ness of sixty fathoms each. 



" 2. The minerals contained in the above mines are blended together 

 so as to produce the appearance of white Italian marble clouded with 

 black, and are so extremely hard and compact as to require blasting 

 with gunpowder, to separate them from the general mass. 



" 3. Those in the Ladywash veins ai'e divided in two equal parts 

 parallel to the sides of the fissure. They may be compared to two 

 slabs of marble, whose polished surfaces are absolutely in contact 

 with each other without the least degree of cohesion. 



" 4. These naturally polished surfaces are not truly flat, but in 

 some degree waved, as if formed by a carpenter's plane, consisting 

 of various members. 



" 5. The two surfaces are generally coloured with lead ore, thinly 



1 The History of the Mineral "Waters of Derbyshire, Lincolnshire, and Yorkshire, 

 hy Thomas Short, M.D., 4to., London, 1734, p. 96. 



^ A View of the Present State of Derbyshire, 1789, vol. i. p. 195. 



3 An Inquiry into the Original State and Formation of the Earth, by John. 

 "Whitehurst, 3rd edition, 1792, London, p. 218, et seq., plate i. 



DECADE III. VOL. IT. — NO. IX. 26 



