162 EFFECTS of HEAT 



peding, the defcent of water from the fea above ; fo that the 

 water which had been driven from the fhells at the bottom, 

 would not return to them, or would return but llowly j and 

 they would be expofed dry to theaction of heat fv 



In this cafe, one of two things would inevitably happen. Ei- 

 ther the carbonic acid of the fhells would be driven off by the 

 heat, producing an incondenfable elaftic fluid, which, heaving 

 up or penetrating the fuperincumbent beds, would force its 

 way to the furface of the fea, and produce a fubmarine erup- 

 tion, as has happened at Santorini and elfewhere; or the vo- 

 latility of the carbonic acid would be reprefled by the weight of 

 the fuperincumbent water (k k), and the {hell-bed, being fof- 

 tened or fufed by the action of heat, would be converted into 

 a ftratum of limeftone. 



The foregoing experiments enable us to decide in any parti- 

 cular cafe, which of thefe two events muft take place, when 

 the heat of the lava and the depth of the fea are known. 



The table mews, that under a fea no deeper than 1708 

 feet, near one-third of a mile, a limeftone would be formed 

 by proper heat \ and that, in a depth of little more than 

 one mile, it would enter into entire fufion. Now, the com- 

 mon foundings of mariners extend to 200 fathoms, or 1200 

 feet. Lord MulgRave f found bottom at 4680 feet, or 

 nearly nine-tenths of a mile; and Captain Ellis let down 

 a fea-gage to the depth of 5346 feet %. It thus appears, 



that 



* This fituation of things, is iimilar to what happens when fmall-coal is moi- 

 ftened, in order to make it cake. The duft, drenched with water, is laid upon the 

 fire, and remains long wet, while the heat below fuffers little or no abatement. 



\ Voyage towards the North Pole t p. 142. 

 % Philofophical Tranfa&ions, 1751, p. 212. 



