130 Mr Forbes's Pht^akal Notices of the Bay of Naples. 



that next Pozzuoli, and gradually rises with rocks of a more 

 massive form to the opposite one. The general whiteness pro- 

 duced by the disintegration of the mineral substances by the 

 action of emitted gases gives the whole rather a dazzling than 

 an imposing appearance. At the east side rise the emissaries 

 of steam and vapour, which show the igneous action to be still 

 in a condition of great activity, and the substances which sur- 

 round them, are coated with the party-coloured salts which are 

 contained in the " fumerole." Some authors, and particularly 

 Delia Torre,* have asserted that flames are to be seen during 

 the night ; but from the account of the best authors, this 

 seems to have been a mistake, at least they were not observed 

 at the close of the last century, when we have the most au- 

 thentic account of this spot. These rise at short distances 

 from one another through the flat crust of which the bottom 

 of the crater is composed, which in almost every part is warm, 

 and in some so much so, as to afford the means of evaporating 

 the aluminous solutions. The water required to form these, 

 we have just noticed is rare, and it was the Abbe Breislak who 

 first devised the means of procuring a sufficient quantity, as 

 we shall presently explain ; but from Sir William Hamilton's 

 account, we are led to believe that the water of La Pisciarella, 

 a spring I have formerly described,-|- and which lies in the di- 

 rection of Agnano, on the exterior side of the crater, was tran- 

 sported here for that purpose. 



The reverberation heard on striking the ground violently 

 has excited some difference of opinion among authors ; many 

 considering it an evidence of a subterranean vault ; but the 

 greater part imputing it to the porous nature of the ground, 

 which, by the approximation of its parts from a sudden blow, may 

 produce the effect. I cannot, however, think the former opi- 

 nion futile ; and I have the satisfaction of having Dr Dau- 

 beny to support me. Mr Scrope, in his paper just publish- 

 ed, X and also in his Considerations on Volcanos, § thinks he has 

 proved that such a cavity can never exist ; yet let us consider 

 how it miffht be formed in the case of the Solfatara : The 



o 



ap^3f of the inverted cone or crater, which is truncated by the 



* Stnrin del Vesuvio. 4- to. Napoli. 



f See this JmrnaJ, last No. p. 261. and No. xiv. p. 265. 



X Geol. Trans, ui sup. p. 345- § P. 267. 



