MODIFIED by COMPRESSION. 163 
that at the bottom of a fea, which would be founded by a 
line much lefs than double of the ufual length, and lefs than 
half ‘the depth of that founded by Lord Mutcrave, lime- 
ftone might be:formed by: heat ; and that, at the depth ‘reach- 
ed by Captain Ex.is, the entire» fufion would be accomplith- 
ed, if the bed of fhells were touched by a lava: at the extre- 
mity of its courfe, when its heat was loweft. Were the heat 
of the lava greater, a greater depth of fea would, of courfe, be 
requifite to conftrain'the carbonic acid effectually; and future 
experiments may determine what depth is required to co-ope- 
rate with any given temperature. It is enough for our prefent 
purpofe to have fhewn, that the refult is. poffible in any .cafe,’ 
and to have circumfcribed the neceflary force of thefe agents 
within moderate limits. - At the fame time it muft be obferved, 
that we have been far from ftretching the known fats; for when: 
we compare the fmall :extent of fea in which any foundings 
can be found, with that of the vaft unfathomed ocean, it is ob- 
vious, that in afluming a depth of one mile or two, we fall 
very -fhort' of the medium.  M. pz La Prace, reafoning 
from the phenomena of the tides, ftates it as highly probable 
that this medium is not lefs than eleven Englifh miles *. 
Iria great part or the whole of the fuperincumbent mafs 
confifted, not of water, but of fand or clay, then the depth re- 
quifite to produce thefe effects would be leffened, in the inverfe 
ratio of the fpecific gravity. If the above-mentioned oc- 
currence took place under a mafs compofed of ftone firmly 
bound’ together by fome previous operation of nature, the 
power of the fuperincumbent mafs, in oppofing the efcape of 
X 2 carbonic 
* “ On peut donc regarder au moins comme trés probable, que Ja profondeur 
“* moyenne de la mer n’eft pas au-deffous de quatre lienes.” .. Dr 1a PLAcE, 
Hift, de lAcad. Roy. des Sciences, année 1776, 
