( '4 ) 



length, and eight in breadth, and wasj like 

 the others, buried in the breccia. 



Thefe five fpecies of volcanic produdions 

 were certainly not natural to the fubftance 

 of the lava ; for their fradures and angles 

 are very vifible, and by carefully breaking 

 the lava they may be extracted entire. We 

 muft therefore conclude that they were ab- 

 forbed and inclofed in the lava when it was 

 in motion, and thus were confolidated into 

 one body. 



In making thefe obfervations a doubt 

 fuggefted itfelf. Though to the naked eye, 

 and likewife to the touch, the vitreous lava 

 appears perfedly fmooth, yet, when viewed 

 with a lens of a ftrong magnifying power, 

 its furface appeared full of very minute fif- 

 fures. At leaft, if this was not obfervable 

 in all, it was in feveral pieces of both thefe 

 kinds of glafs, I therefore conjectured, that 

 when thefe fubftances were in an ignited 

 ftate, a current of water might have paiTed 

 over them j or that they fuddenly came in 



conta^ 



