MODIFIED ly COMPRESSION. 159) 
paper, prove, that the feebleft exertions of volcanic fire, are of 
fufficient intenfity to perform the agglutination, and even the 
entire fufion, of the carbonate of lime, when its carbonic acid 
is effectually confined by preflure; for though: lava, after its. 
fufion, may be made, in our experiments, to congeal into a 
glafs, in a temperature of 16° or 18° of WEDGwooD, in which 
temperature the carbonate would fcarcely be affected ; it muft 
be obferved, that a fimilar. congelation is not to be looked for 
in nature ; for the mafs, even of the fmalleft ftream of lava, is. 
too great to admit of fuch rapid cooling. And, in fact, the 
external part of a lava is not vitreous, but confifts of a fub-- 
ftance which, as my experiments have proved, muft have been. 
congealed in a heat of melting filver, that is, in 22° of WEDG- 
woop ; while its internal parts bear a character indicating that 
they congealed in 27° or 28° of the fame fcale. It follows, 
that no part of the lava, while it remained liquid, can have 
been lefs hot than 22° of WepGwoop. Now, this happens to 
be a heat, in which I have accomplifhed the entire fufion of 
the carbonate of lime, under preflure. We muft therefore 
conclude, that the heat of a running lava is always of fufh-. 
cient intenfity to perform the fufion of limeftone. 
In every active volcano, a communication muft exift between. 
the fummit of the mountain and the unexplored region, far 
below its bafe, where the lava has been melted, and whence it 
has been propelled upwards ; the liquid lava rifing through this 
internal channel, fo-as to fill the crater to the brim, and flow. 
over it. On this occafion, the fides of the mountain muft un- 
dergo a violent-hydroftatical preffure outwards; to which they 
often yield by the formation of a vaft rent, through which the. 
Java is difcharged in a lateral eruption, and flows in a continued. 
ftream fometimes during months. On /itna moft of the erup- 
tions are fo performed; few lavas flowing from the fummit, 
but generally breaking out laterally, at very elevated ftations.. 
2 Ne At. 
