810 



THE WONDERS OF GEOLOGY. Lect. VIH. 



5. The Phlegr^ean Fields and Lipari Isles. — The 

 volcanic region of Naples consists of a linear group of 

 cones, ranging N.E. and S.W., and terminating at either 

 extremity by the two principal mountains, Ischia and 

 Vesuvius ; the latter seems to be connected by the inter- 

 vention of minor vents with the group of Albano and of 

 Rome ; the seven hills of the Eternal City being volcanic 

 mounds.* 



The district of Puzzuoli and Cumse, on the Bays of Baiae 

 and Naples, is called the Phlegraean Fields, and in it are 

 situated Monte Nuovo, Monte Barbaro, the Solfatara, and 

 the Temple of Serapis. This tract presents a series of cones 

 and crateriform basins ; some of which contain lakes, as 

 those of Avernus and the Lucrine. These volcanic mounds 

 are formed of felspathic tufa, occasionally containing marine 

 shells and carbonized wood, and are covered by beds of 

 loose tufaceous conglomerate. They are supposed by 

 Mr. Scrope to have been produced by numerous sub- 

 marine eruptions, each from a fresh focus, on a shallow 

 shore, f 



The volcanic cone termed the Solfatara, so well known 

 from its incessant emission of torrents of aqueous and sul- 

 phurous vapour, through superficial fissures, is recorded as 

 having been in a state of activity in the year a.d. 1180. 

 Mr. Scrope supposes the present crater to have been formed 

 at that period ; and he attributes the constant emanations 

 of sulphuretted hydrogen, to the effect of a mass of lava still 

 existing beneath at an intense temperature. The chemical 

 changes effected by the immediate conversion of this gas 

 into sulphuric acid, from combination with the oxygen of 

 the atmosphere, and the subsequent action of the acid on 

 the tufas, trachytes, &c, giving rise to sulphates of alumine, 

 iron, lime, magnesia, soda, &c. ; while the silex is left nearly 



* Mr. Scrope, Geol. Trans, vol. ii, p. 337. 

 f Scrope on Volcanoes, p. 179. 



