226 Fluids in the Cavities of Minerais: 
dilated condition of the included air, I shall content myself 
with stating, that the facts described in the preceding paper 
appear to me decidedly hostile to the igneous origin of crys- | 
tals, and in some points of view, favourable to their aqueous 
formation." The existence of a fluid which entirely fills thé 
cavities of crystals, at a temperature varying from 74° to 84° 
“ may, upon the principles assumed in the opposite argument, 
be held as a proof that these crystals are formed at the ordi- 
nary temperature of the atmosphere, while the fact of a per- 
fect vacuity existing in sulphate of barytes, and capable of 
being filled up by the expansion of the aqueous fluid, ata 
temperature not exceeding 150°, authorises the analogous 
conclusion, that the crystal could not have been formed at a 
higher temperature. On the other hand, the filling up of the’ 
vacuities in sulphate of iron, and sulphate of nickel, at atem- 
perature much above that at which they were formed, may 
lead geologists to renounce a species of argument which ap- 
peals only to our ignorance, and to withdraw from the ¢ 
fence, even of their outworks, those faithless auxiliaries which 
are so ready to enlist themselves in the service of either power. 
_ There is one geological relation, however, of the preced- 
ing facts, which may deserve some attention. Hitherto the 
contending theorists have limited their idolatry to two of the 
elements ; but the existence of two new substances in mine- 
aqueous hypothesis. 
Had the two new fluids occurred only in one mineral, or in 
minerals of a particular composition, they might have been 
_ Sapposed to have some relation to the elementary principles 
of the body, and to have arisen either from some accidents 
ety, which prevented them from crystallizing, OF 
om the decomposition of the matter subsequently to its crys- 
ee ie the perfect identity, however, of ahe two fluids, 
as found im pure Quartz, in Amethyst, in Topaz, and in Cy> 
