INDEX. 351 



, a fiflure or vein, croffing a lava rock, filled with bolus, 

 copperas, and magnefe, 6. 



often found in the fitfures of limeftone rock, 45. 51. 



nay, often between the calcareous beds, 51. 47. 49. 



its hard fubftance, though vitreous and hard, and its 

 black or grey colour, by fulphureous acid fleams of the 

 Solfatara changed into white and aluminous clay, 16^. 



236. 

 its form. 



a. Pointed irregular prifmatic. See vitreous Lava. 

 I. Columnar prifmatic, under calcareous marine beds, 



49- 



See Bafaltcs. 



c. Globular concentric, 236. 

 d. Cubic and rhombo'idal. 



See Porphyry. 



- Its varieties, fubjtance, mixture^ colour. 

 A. Vitreous, erroneouily, and commonly called Iceland 



agate. 

 j. Black. 



a. $>emi-tranfparent y a perfect glafs. 



from Iceland, naturally fplit into irregular 



pointed prifms, 158. 



1. "Black and dark, a perfect glafs. 

 from monte Caiajo, 15. 

 from Sardinia, 312. 



from Ifchia, 177. 



from Montagna di S. Fiore, 242. 



from Vefuvius. 



a. With hexagonal white fherl cylinders, '1^7, 



158. 

 0, With white fherl ftari. 



7. With 



