208 ACTIOJ? OF HEAT MODIFIU) 



The foregoing experiments enable us to decide in any parti- 

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

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

 Applicaticn of The table shews, that under a sea no deeper than 17OS feet^ 



thepi;eeediug ^^^^ one- third of a mile, a limestone would be formed by 

 experiments to ' J 



determine the proper heatj and that, in a depth of little more than one mile, 



l"in"^on"° it would enter into entire fusion. Now, the common sound- 

 ings of mariners extend to 200 fathoms, or 1200 feet. Lord 

 Mulgrave* found bottom at 46"S0 feet, or nearly nine-tenths 

 of a mile ; and Captain Ellis let down a sea-gage to the depth 

 It might be of 5346 feet. f It thus appears, that at the bottom of a sea, 

 than double the ^^'''"^ would be sounded by a line much less than double of 

 tasual depth of the usual length j and less than half the depth of that sounrled 

 '° ■ by Lord Mulgrave, limestone might be formed by heat ; and 

 that, at 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 gr&ater depth of sea 

 would, of course, be requisite to constrain the carbonic acid 

 effectually ; and future experiments may deteimine what deptli 

 is required to co-operate with any given temperature. It is 

 enough for our present purpose to have shewn, that the result 

 is possible in any case, and to have circumscribed the necessa- 

 ry force of these agents within moderate limits. At the same 

 time it must be observed, that we have been far from stretch- 

 ing the known facts ; for when we compare the small extent 

 of sea in which any soundings can be found, with that of the 

 vast unfathomed ocean, it is obvious, that in assuming a depth 

 of one mile or two, we fall very short of the medium. M. de 

 la Place, reasoning from the phenomena of the tides, states it 

 as highly probable that this medium is not less than eleven 

 English miles.]: 

 less depths If a great part or the whole of tlie superincumbent mass 



the"same pres- coniisted, not of water, but of sand or clay, then the depth re- 

 * Voyage towards the North Pole, p. 149. 

 t Philosophical Transactions, 1751, p. 212. 

 X " On pent done regarder an moins comme tr&s probable, que 

 " la profondci^r nioyenne de la mer n'cst pas au-dessous de quatre 

 " lieues." De la Place, Uist. de V Acad, Roy.des Sciences, annee, 

 1776. 



quisite 



