{ 2S6 ) 



on the others ; not excepting the bafe of 

 thofe I have termed breccias ; and I ob- 

 tained from them the fame kind of grey 

 and cellular enamel. 



I have called the lavas now defcribed 

 pitch-ftone lavas, becaufe they refemble in 

 their external appearance the ftone defigned 

 by that name. I have likev\^ife the autho- 

 rity of M. Dolomieu, who treating of lavas 

 found by him in the Paduan mountains, 

 and in the iflands of Ponza, gives them 

 that denomination. He afferts, however, 

 that the lavas differ from the pitch-ftone in 

 a peculiar property, which confifts in the 

 extreme eafe with which the volcanic pitch- 

 ftones may be fufed, and the infufibility 

 of the true pitch-ftone even In a violent 

 fire *. 



Having obtained a number of pltch- 

 ftones that were not volcanic, I determined 

 to make experiments on them in the fur- 



* In his Notes to Bergmann's DifTertatlon on Vol- 

 canic Produds. 



nace. 



