Fluids in the Cavities of Minerals. 225 
xtended and contracted ‘itself as before. This wa S owing to 
the moisture of the hand; and our author could at any time 
revive the indurated stubstanice, by the approach of a moist 
body. <A portion of the fluid, which was taken out of a cav 
ity twenty days ago, is still capable of being restored to a fluid 
state by moisture. This portion was shown to an eminent 
naturalist, the Rev. Dr. Fleming, of Flisk, who remarked, 
that had he observed it accidentally, he would have ascribed 
its apparent vitality to the movements of some of the ani- 
mals of the genus Planaria. 
After the cavity has remained open for one or two davs, 
the second fluid comes out of it, and hardens very speedily 
into a yellowish resinous-looking ge ge which is perfect- 
transparent. ‘This substance absorbs moisture, but with 
less avidity than the other. It is not vabatilined by heat. - It 
is not soluble in water or alcohol ; but it is rapidly dissolved 
with effervescence by the sulphari¢ acid. The nitric and mu- 
riatic acids also dissolve 
The residue of the first fluid is volatilized by heat; and it 
is also dissolved, but without effervescence, by the sulphuric, 
the nitric, and the muriatic acids. After standing some time, 
oth these substances acquire a brilliant lustre, as if some 
metallic body entered into their composition. 
It would be improper to conclude this paper, says our au- 
thor, without noticing the relations which are supposed to 
subsist between this class of phenomena and the two contend- 
ing Geological Theories. The existence of highly rarified 
gas in the cavities of crystals, has been regarded by the dis- 
tinguished President of the Royal Society of London, as 
** seeming to afford a decisive argument in favour of the ig- 
neous ori of crystalline rocks ; ;” and the “ fact of almost 
a perfect m existing in a cavity containing an expansi- 
ble but difficultly volatile substance,” (as naphtha,) he like- 
wise considers as highly favourable to the same theory. The 
discovery of compressed gas in similar cavities might have 
arded as neutralising in some degree the first of these 
arguments: but Sir Humphrey Davy remarks, that it may 
be explained, by supposing y the erystal to have been formed 
under a compression much more than adequate to compen- 
sate for the expansive effects of heat. 
Without presuming to combat these deductions, or to s 
gest any of the numerous explanations by which the Neptus 
nist sa nem with his own system the compressed and 
VOL. XII. NO, 29 
