( 3it ) 



fatlsfied that it muft, as well as the pitch- 

 flones of the ifles of Ponza, from the ob- 

 fervations of Dolomieu. According to this 

 author, the fimilar kinds of lavas found in 

 thefe two countries have for their bafe the 

 feltfpar, with a very confiderable quantity 

 of magnefia * ; and, in a note to his work 

 on the iflands of Ponza, fpeaking of the 

 Vicentine lavas, he remarks, that he found 

 among them fome produdtions of pitch- 

 ffcone, which he could not confider as a 

 true volcanic produd:, but rather as a con- 

 cretion formed afterwards by the decompo- 

 fition of volcanic matters ; and that they 

 contained a great quantity of magnefia* 

 From which we may gather that magnefia, 

 in the opinion of this author, is one of the 

 conftituent principles of the pitch-ftones 

 of volcanos. The truth however is, that 

 in the three analyfes above mentioned, of 

 the pitch-ftone lavas of the mountains of 

 Sieva and Bajamonte, two of the Euga- 

 cean mountains, J did not find an atom of 

 this earth, 



* Notes on Bergmann. 



X 4 The 



