536 Mr R. ALLAN on a Suite of Volcanic Rocks 



Some of these crystals are extremely beautiful, branching out to 

 the extent of several inches, and frequently presenting the most 

 fantastical shapes. 



The remainder of the suite are the productions of the island 

 of Vulcano; most of them having been collected within and around 

 the margin of its crater. 



No. 34. is either the obsidian of the year 1775, which DOLO- 

 MIEU tells us flowed over the side of the crater in a stream ; or 

 that produced during the last eruption in 1786. I found it about 

 half way up the mountain, generally in large broken masses, but 

 in several places also distinctly forming very extensive surfaces. 

 It is the blackest and most vitreous variety on the island, and, 

 judging from the lengthened shape of the cavities interspersed 

 throughout it, must have flowed quickly, and cooled rapidly. 



No. 35. is the common variety of obsidian from this locality. 

 It is neither so compact, so translucent, nor so vitreous as the 

 Lipari species, and has much more the aspect of pitchstone, than 

 of obsidian. 



No. 36. This is an interesting piece, as exhibiting clearly 

 the gradation between obsidian, pitchstone, and pumice. One 

 portion of it is closely allied to the last specimen, while another 

 has equally near relation to the next. 



No. 37. The common pumice of the island of Vulcano, where, 

 however, it is by no means of so fine a quality as in Lipari ; and 

 where it is never worked for any commercial or useful purpose. 



No. 38. is a variety of the coarse pumic containing an im- 

 bedded mass of obsidian. The remaining specimens were all 

 collected within the crater. With one of the men employed in 

 gathering the sulphur, I descended by a rugged and circuitous 

 path, but with comparative ease, about 400 feet into the smoking 

 abyss ; and examined its surface with perfect facility. 



No. 39. is the kind of porcelain jasper peculiar to this loca- 

 lity, and occurring in great abundance inside the crater. 



