264 Mr Forbes's Physical Notices of the Bay of Naples. 



Its circumference has been estimated at 2^ *, 3 f , 4J J, and 6 

 miles §. We shall not probably go far wrong if we consider 

 the road made round the bottom 2J miles, and the circumfe- 

 rence at top 4. Its depth is very considerable, and the sides 

 precipitous, and even overhanging. Part of the edge of the 

 crater is cut down to facilitate the descent at one place, which 

 is still very steep. It affords an interesting section represented 

 by Hamilton, Plate xix. This spot must once have been 

 the seat of continued volcanic fires at a period subsequent to 

 the formation of the tufaceous hills below, and, I have little 

 doubt, subsequent also to the retirement of the waters of the sea. 

 This seems demonstrated by the absence of the degrading ef- 

 fects of water ; and Astroni is happily placed among the sur- 

 rounding eminences, to exhibit the two conditions of ancient 

 and immemorially extinct volcanos. I give it merely as a 

 hint, not being qualified to speak from experience on the com- 

 parison, that perhaps Astroni has a geological antiquity resem- 

 bling that of the extinct volcanos of the Vivarais, beyond the 

 memory of man, but similar in constitution to craters which 

 have suffered recorded paroxysms, such as the Solfatara in 

 1198. 



In conformation, this crater exhibits not merely tufa and 

 pumiceous conglomerates, but beds of real lava. Breislak 

 seems to say, that obsidian is to be reckoned among the pro- 

 duction^of Astroni || ; but I did not meet with any, and it is 

 not usually mentioned. " He also particularly notices a beau- 

 tiful siliceous incrustation, which, from his description, must, 

 I think, be fiorite. Both this substance and obsidian occur in 

 the Island of Ischia. As we have already noticed that the 

 walls of the crater are precipitous, so the bottom is flat and 

 extensive, upon which rise several parasitic cones, as Scrope 

 terms them ^, three of which ate transformed into lakes. The 

 distinctness of these phenomena are sufficient to prove the later 

 date of this volcanic crater. It has been asserted that there 

 are mineral springs here which supply the lakes, particularly 



• Eustace. t Breislak and Daubeny. t Starke- § Hamilton. 

 II " L'interieure de ce cratere abonde en verresnoirs, qu'un principe de 

 decomposition rend ties fTagihs."'—Campanie^ ii. 64>. 

 % See his Considerations on Volcanos, p. 165. 



