EXPERIMENT'S on WHINSTONE and LAVA. 63 



pied by large air holes, which do not appear to have contained 

 any extraneous matter. 



It produced a very fufible glafs, from which was formed a 

 cryftallite much more refractory than the original. 



No. 5. Lava of Torre del Greco. 



This lava, which flowed from Vefuvius to the fea in the 

 middle ages, has been an object of much attention, on account 

 of its confpicuous bafaltic form. It confifts of a grey bafis, the 

 fracture of which is coarfe and rough, and in which are embed- 

 ded large and well characterized cryftals of fchorl, (augit), with 

 a few chryfolites, (olivins). 



It was found to be lefs fufible than any of the others, yet its 

 glafs cry ft alii zed in a lower temperature. 



No. 6. Lava of Vefuvius, eruption 1785. 



From the circumftances in which the above five lavas have 

 been feen to cryflallize after fulion, it can fcarcely be doubted 

 that the fame procefs takes place in a volcanic ftream, which, 

 in confequence of its bulk, muft cool with confiderable flow- 

 nefs, and that a vitreous character would be affumed by the 

 whole mafs, were it cooled with fufEcient rapidity. 



The truth of this laft opinion is demonftrated by fome facts 

 which I accidentally obferved, long before my prefent views had 

 occurred, when, in fpring 1785, I had an opportunity of exa- 

 mining a ftream of lava, which flowed from Vefuvius. The 

 eruption was comparatively fo gentle, that I was able, though 

 not without inconvenience, to approach and examine the fiery 



ftream 



