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ncceflary to produce prifms cannot take 

 place. But many currents which defcend 

 from the fummit of burning mountains to 

 the fea, muft have loft their eftervefcence 

 with their heat in fo long a courfe, and 

 fcarcely contain fufficient to continue their 

 motion downwards, which, perhaps, would 

 ceafe, were it not for the impelUng gravity 

 of the lava, which frequently falls into the 

 fea perpendicularly. 



Such is the hypothefis by which I would 

 explain the caufe why fome lavas have afr 

 fumed a prifmatic conformation without 

 any concurrence of the fea-water, and 

 others exhibit no appearance of it in places 

 where they have immerged into the fea. 

 I neverthelefs leave every one to form his 

 own opinion ; and fhould an explanation 

 of thefe important fadts be difcovered, pre- 

 ferable to mine, which I confider as only 

 conjectural, I fhall receive the communica- 

 tion of it with fmcere gratitude, and adopt 

 it with pleafure. 



P4 CHAP. 



