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exceeded the two other princIpTes, and there- 

 foremuftbeconfideredasthebareof the ftone, 

 wa& in fmall maffes of unequal furface, lamel- 

 lar in the fradlures, tranfparent in the angles, 

 and of a changeable milky whitenefs. Nei- 

 ther of the three principles has a determi- 

 nate fortn of cryftallization. I think I fhall 

 not be miftaken if I aiTert, that this granite 

 has not fafFered the action of the fire. In 

 fad, a continuance of a quarter of an hour 

 IB the furnace produced in it fo great an 

 slteralion, that every part of it was fenfibly 

 changed. The mica became pulverable, the 

 quartz extremely friable and full of cracks, 

 and^ lofmg its tranfparency and vitreous 

 brilliancy, became entirely white. The felt- 

 fpar^ likewife, contra<3:ed a confiderable fri- 

 ability J lofmg at the fame time its change- 

 able colour, and becoming whiter. It is not 

 therefore extraordinary that a flight blow 

 with a hammer fhould now break this flone 

 into fmall pieces ; though before it would 

 only ftrike off, at moft, a fjngle fragment. 

 When expofed to the furnace for feveral 

 days fucceiTively, the quartz and mica did 



not 



