EXPERIMENTS on WHINS'fONE and LAVA. 47 



fame caufe, and to believe that whinftone, as well as lava, has 

 been expofed to the action of heat. In the courfe of the paper, 

 I mall mention feveral accidental remits, which, if confidered 

 feparately, might feem unworthy of notice, but which, by af- 

 fording the means of comparifon between the two clafTes, are 

 of great fervice in the general inveftigation. 



The whinftone firft employed was taken from a quarry* near 

 the Dean, on the Water of Leith, in the neighbourhood of 

 Edinburgh. This ftone is an aggregate of black and green- 

 ifh-black hornblend, intimately mixed with a pale reddifh- 

 brown matter, which has fome refemblance to felfpar, but is 

 far more fufible. Both fubftances are imperfectly and con- 

 fufedly cryftallized in minute grains. The hornblend is in 

 the greateft proportion ; and its fracture appears to be ftriated,. 

 though in fome parts foliated ; that of the reddifh-brown 

 matter is foliated. The fracture of the flone en majje. is uneven, 

 and it abounds in fmall facettes, which have fome degree of 

 luftre. It may be fcratched, though with difficulty, by a knife, 

 and gives an earthy fmell when breathed on. It frequently 

 contains fmall fpecks of pyrites. 



On the 17th of January 1798, I introduced a black lead cru- 

 cible, filled with fragments of this ftone, into the great reverbe- 

 rating furnace at Mr Barker's iron foundery. In about a 

 quarter of an hour, I found that the fubftance had entered into 

 fufion, and was agitated by a flrong ebullition. I removed the 

 crucible, and allowed it to cool rapidly. The refult was a black 

 glafs, with a tolerably clean fracture, interrupted however by 

 fome fpecks. 



In fubfequent experiments, I endeavoured, by flow cooling 



after fufion, to prevent the whinftone from becoming vitreous, 



and to compel it to refume its original character by cryftalliza.- 



tion. In this I fo far fucceeded as to obtain a fubftance, 



which was not glafs, though it did not poftefs the properties 



of 

 * Called Bell's Mills Quarry, 



