SS gee ae ee En wer Waa 
Ee 
seit == 
SEE OS SR ae Se nee 
ee ae? 2 
Mineralogy and Geology. 431 
the crystals ; and all appeared to have been corroded as by some solvent. 
This solvent must have reached the fluor after the quartz crystals were 
formed about them, and the resulting solution passed off at the same 
time. Some contained translucent fragments of carbonate of iron along 
with the fluor. 
The specimens of quartz to which the crystals were attached con- 
sisted of successive layers of different colors, and appeared to have been 
formed by depositions at distinct intervals. At another time, an entire 
change of condition must have occurred in the vein, in which octahedral 
crystals of fluor were formed on the quartz. Again silex was deposited 
on the fluor; and then fluor again upon the quartz. These processes 
appear from some of the crystals to have been several times repeated, 
and then came a coating of silex on the fluor, apparently in many succes- 
sive depositions. 
Mr. Fox supposes that these changes have taken place through the 
action of steam, which may exist in fissures below the water at great 
depths, from the agency of internal heat ; and the alternate depositions 
may have proceeded from the struggle which would take, place between 
the steam and water above, the one encroaching at intervals on the 
other. These views are thus presented :-— 
I have, on former occasions, alluded to yarious causes which would 
produce circulation in the subterranean waters, such as the opening or 
closing of any portions of fissures; the ascent of warm, and the descent 
of cooler currents of water, in consequence of the differences in their 
specific gravities; or in some instances, by the pressure of sea water 
acting on the fresh. Nearly two years ago, I stated in this room, my 
views in reference to the operation of this latter cause on land springs ; 
and at the same time, I attempted to show the possibility, not to say 
probability, of steam existing in fissures below the water at a very great 
depth. I may, perhaps, be permitted to refer again to this subject, be- 
cause it appears to me to be one of some interest. I then took it for 
granted that the temperature of the earth increases, in some proportion 
to the increase of the depth below its surface ; and that if the ratio be 
taken at 1° Fah. for every 48 feet, as found in our deep mines; and if 
Le Roche’s data for calculating the elastic force and density of steam be 
adopted, the forces of steam and of water pressure would balance each 
other at rather more than nine miles deep, each being equal to the 
pressure of more than 1400 atmospheres. The density of the steam 
would there be about one-fourth that of water at 60° Fah., and its tem- 
perature above 1050° Fah. But the temperature may probably not in- 
crease so rapidly as this at great depths, and the equilibrium in the 
pressures of the column of water and of steam, may occur much further 
below the surface, where the density of steam, under an augmented 
