198 Effects of Heat modified hy Compression. 



power of stopping, or of very much impeding, the descent 

 of water from the sea above; so that the water which had 

 been driven from the shells at the bottom would not return 

 to them, or would return but slowly ; and they would be 

 exposed dry to the action of heat *. 



In this case, one of two things would inevitably happen : 

 either the carbonic acid of the shells would be driven off by 

 the heat, producing an incondensable elastic fluid, which, 

 heaving up or penetrating the superincumbent beds, would 

 force its way to the surface of the sea, and produce a sub- 

 marine eruption, as has happened at Santorini and else- 

 where, or the volatility of the carbonic acid would be re- 

 pressed by the weight of the superincumbent water (kk), 

 and the shell-bed, being softened or fused by the action of 

 heat, would be converted into a stratum of limestone. 



The foregoing experiments enable us to decide in any par- 

 ticular case, which of these two events must take place when 

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



The table shows, that under a sea no deeper than 1708 

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

 by proper heat; and tha^ in a depth of little more than one 

 mile, it would enter into entire fusion. Now, the common 

 soundings of mariners extend to 200 fathoms, or 1200 feet. 

 Lord Mulgravef found bottom at 4630 feet, or nearly nine- 

 teuths of a mile; and captain Ellis let down a sea-gage to 

 the depth of 534fi feet J. It thus appears, that at the bot- 

 tom of a, sea which would be sounded by a line much less 

 than double of the usual length, and less than half the depth 

 of that sounded bv lord Mulgrave, limestone might be formed 

 by heat ; and that aft the depth reached by captain Ellis, the 

 entire fusion would be accomplished, if the bed of shells 

 were touched by a lava at the extremity of its course, when 

 its heat was lowest. Were the heat of the lava greater, a 



* This situation of things is similar to what happens when small-coal is 

 moistened; in order ro make it cake. The dust, drenched with water, is laid 

 upon the fire, and 'emains long wet, while the heat below suffers little or no 

 abatement. 



t Voyage towards the North Pole, p. 142. 



} Philosophical Transactions 1751, p. 212. 



greater 



