( 209 ) 



** frequently found polyhedrous bafaltes 

 " perfcdly charadterized in excavations 

 *' made by men in the centre of lavas, 

 " which have iflued from the fides of 

 " Mount Etna, in periods much pofterior 

 " to the retiring of the fea." 



I jfhould, however, appear deficient in 

 candour, did I not mention that M. Dolo- 

 mieu admits that lavas may fometimes, 

 in the air, aflume the prifmatic form, if 

 they fall into clefts and fiffures where they 

 fuddenly cool, of which he adduces an ex- 

 ample in the iflands of Ponza. 



I {hall only remark, that I do not per« 

 ceive the abfolute neceffity of the fiffures 

 in this cafe ; fmce we frequently find lava3 

 with this configuration in perfe<ftly open 

 places ; as I have feen in the great mouth 

 of Vulcano. And with this opinion the 

 obfervations of Gioeni on Etna certainly 

 accord ; for, had he remarked the concur- 

 rence of fuch a circumftance, he, undoubt-f 

 cdly, would have mentioned it. 



VOL. III. P What 



