EXPERIMENTS on WHINSTONE and LJFJ. 47 



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

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

 I fhall mention feveral accidental refuks, which, if confidered 

 feparately, raight feeni unworthy of notice, but which, by af- 

 fording the means of comparifon between the two claffes, are 

 of great fervice in the general inveftigation. 



The whinftone iirft 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- 

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

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

 far more fufible. Both fubltances are imperfedtly and con- 

 fufedly cryftallized in minute grains. The hornblend is in. 

 the greateft proportion ; and its fracflure appears to be ftriated, 

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

 matter is foliated. The fra(5ture of the flone en majfe 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 \yhen 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 ftrong ebullition. I removed the 

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

 glafs, with, a tolerably clean fradlure, inteiTupted 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 charader by cryftalliza- 



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



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



of 

 * Called Bell's Mills Qiiarrj-. 



