MODIFIED ty COMPRESSION. 16% 
preflure would in all cafes, efpecially where the depth was confi- 
derable, far furpafs what it would have been under an equal 
depth of water. Where the depth of the ftream, below its 
point of delivery, amounted, then, to 1708 feet, the preflure, if 
the heat was not of exceflive intenfity, would be more than fuf- 
ficient to conftrain the carbonic acid, and our limeftone would 
fuffer no calcination, but would enter into fufion; and if the 
eruption ceafed at that moment, would cryftallize in cooling 
along with the lava, and become a nodule of calcareous {par. 
The mafs of lava, containing this nodule, would then conftitute 
a real whinftone, and would belong to the ‘kind ‘called amygda- 
loid. In greater depths ftill, the’ preffure would be propor- 
tionally increafed, till fulphur, and even water, might be con- 
ftrained ; and the carbonate of lime would continue undecom- 
pofed in the higheft heats. 
Ir, while the lava was in a liquid ftate, during the eruption 
or previous 'to it, a new rent (de, fig.41.), formed in the folid 
country below the volcano, was met by our ftream (at d@), it is 
obvious that the lava would flow into the aperture with great 
rapidity, and fill it to the minuteft extremity, there being no 
air to impede the progrefs of the liquid. In this manner, a 
ftream of lava might be led from below to approach the bot- 
tom of the fea (ff), and to come in conta@ with a bed of 
loofe’ fhells (¢¢), lying on that bottom, but covered. with — 
beds of clay, interftratified, ‘as ufually occurs, with beds of 
fand, and other beds of fhells. The firft effe&t of heat would be 
to drive off the moifture of the loweft fhell-bed, in a ftate of va- 
pour, which, rifing till it got beyond the reach of the heat, 
would be condenfed into water, producing a flight motion of 
ebullition, like that of a veffel of water, when it begins’ to 
boil, and when it is faid to fimmer. The beds of clay and fand 
might thus undergo fome heaving and partial derangement, but 
would ftill poflefs the power of ftopping, or of very much im- 
Vou. VI.—P. I. xX peding, 
