( 213 ) 



to fay the truth, appears to be fufEclent, 

 with fome requifite modifications ? Thefe 

 I will endeavour to fuggeft, illuftrating 

 my conjed:ure by the two cafes above ad- 

 duced ; the one, that of the lavas which 

 take the form of prifms merely from the 

 conta<3: of the atmofphere, as in Vulcano 

 and near the fummit of Etna ; the other, 

 that of the lavas which refufe to take fuch 

 a form even within the fea, as at Ifchia, in 

 fome parts of the bafe of Etna, and in all 

 the Eolian ifles except Felicuda. 



As to the former, may not a fudden 

 coagulation and contradion have taken 

 place in fome lavas from the mere influence 

 of the atmofphere, though the lava was 

 not included in any cleft or fiflfare ? It 

 is fufficient that it be fuddenly deprived 

 of the caloric (heat) by which it is pene- 

 trated, and which rendered it rarefied and 

 fluid. To this deprivation a lava of little 

 thicknefs will be very liable ; fmce a body 

 iofes its heat the fooner, the lefs its thick- 

 nefs and denfity. This fudden contradion 

 P 3 may 



