No. VII. — Islands of Procida and IscMa. 339 



ground is covered with loose fragments of pumice and obsi- 

 dian, which I did not succeed in tracing to their source." 

 Castiglione is situated between the town of Ischia (or Celso,) 

 and Casamicciola, as the context implies, and it was indeed 

 there that I myself met with large specimens of this substance, 

 and was informed by my guide, (a native of the island,) that 

 it was found in considerable quantity farther inland. With 

 regard to its origin, the account of Spallanzani may give us 

 full satisfaction, for in the English translation of the work of 

 that able observer, enamels mean nothing else than obsidian, 

 which he describes as being found in this spot in strata from an 

 inch to a foot and a half or even two feet thick, accompanied by 

 abundance of pumice, the whole being the distinct production 

 of a crater in the neighbourhood named Rotaro, (which seems 

 to be Le Cremate of some authors.) The pumice he describes 

 as fibrous, occurring in large masses, and extending more than 

 a mile. It is fitted for all the purposes of the pumice of com- 

 merce. Spallanzani justly says, that the eruption by which 

 these were formed must have been of a slimy nature; the mass 

 of obsidian which I examined, and which was of considerable 

 size, had the most perfectly vitreous character, but was inter- 

 sected by veins and striae of clay, which had obviously once 

 been of a plastic consistence, and the small specimen of it 

 which I still possess displays the same structure. The explo- 

 sion of the Rotaro must therefore have been accompanied with 

 water in such quantity, as to have partly dissolved and car- 

 ried along with it the strata of aluminous clay of this neigh- 

 bourhood, which, as nearly as I remember, perfectly resem- 

 bles the substance united with the volcanic products. It is 

 not a little surprising that the obsidian of Ischia, a mineral so 

 rare in the Bay of Naples, but here so abundant, should have 

 been omitted by so many wrfters ; even the minute Rreislak 

 seems to have passed it over, though so attentive to its rare 

 occurrence elsewhere, as also a small work by Siano, expressly 

 on this island, which professes to give an account of its mineral 

 productions. 



The substance we have next to notice is one which has been 

 entirely overlooked by almost every writer, as far as regards 

 its occurrence here, which is, I confess, attended with some 



