532 Mr R. ALLAN on a Suite of Volcanic Rocks 



In so far as I remarked in the island of Lipari, the large and 

 more continuous tracts of obsidian formed the lower strata, while 

 those of a more pumaceous aspect appeared invariably at a 

 higher level. The purest, blackest, and most beautiful speci- 

 mens, however, are found in nodules in the upper portions of the 

 pumice, where they occur in masses from two inches to as many 

 feet in diameter. The two first specimens are from a locality of 

 this description, occurring perhaps 1000 feet above the level of 

 the sea, among the fine white stratified pumice of that portion of 

 the island called Campo Bianco. 



No. 1. is a specimen of the compact, conchoidal, black obsi- 

 dian, for which, among mineralogists, the Lipari Islands have so 

 long been a celebrated locality. It is translucent on the edges, 

 presents a perfectly vitreous fracture, and is only found in 

 boulders or masses imbedded among the pumice. 



Some portions of this obsidian are less compact, and in No. 2. 

 we remark indications of a more slaggy structure, with several 

 white veins intersecting the black surface in a very beautiful 

 manner. 



The succeeding specimens of the series were collected in less 

 elevated positions, from the obsidian in situ. They are all more 

 or less impure ; some of them exhibiting a very vitreous aspect, 

 others a more earthy, and even a pumaceous appearance. None 

 of them are so perfectly black and compact as the obsidian 

 boulders which occur among the pumice, but they have all in 

 some way or other a close analogy to them. 



No. 3. deviates the least from the pure black obsidian of the 

 two last. It is as nearly as possible the same substance, but is in- 

 terspersed throughout with small white opake globules, which 

 frequently appear stratified, as if formed parallel to the faces of 

 the bed. 



Nos. 4. and 5. are specimens of the stratified obsidian, which 

 have more of an ash-grey appearance, and consist of alternate 



