Mr. It. W. Fox on Pseudomorphous Crystals q/Quaais.r-9 



be denser than at any deeper station, for it would be continu- 

 ally diminishing in density in descending further, from the 

 augmentation of the temperature of the earth, because the ex- 

 panding influence of the increasing heat would much exceed 

 the condensing influence of the extended column of steam, 

 added to that of the nearly constant column of water. 



The line of demarcation between the water and steam would, 

 doubtless, conform in some degree to the inequalities of the 

 surface. It may be difficult at first to conceive the steam ca- 

 pable of supporting the water, or rather of existing perma- 

 nently under it; but this difficulty will, I think, be obviated 

 by the consideration, that the points of contact may be, for the 

 most part, in very narrow fissures, or mere cracks in the rocks; 

 and that the water being greatly heated, may be much less 

 than four times the density of the steam in immediate contact 

 with it. A continual struggle would, no doubt, exist between 

 the water and steam under such circumstances, so that in 

 many places they would alternately encroach beyond the line 

 of demarcation ; but as the checks on both would increase in 

 proportion to the extent of their encroachments from the di- 

 minution of the temperature above and its augmentation below, 

 such encroachments would probably not be very extensive, or 

 of long duration under ordinary circumstances. Supposed 

 temporary encroachment of the water on the limits of the 

 steam to occur at one point, the steam would probably en- 

 croach on the water at another at the same time, and then, 

 inactions taking place, the effects would be reversed. Thus, 

 assuming what indeed would appear to follow from admitted 

 data as necessary consequences, steam would not only exist 

 below the water, but such oscillations would tend to give mo- 

 tion and activity to the water in the neighbouring fissures, 

 causing it to circulate in the earth more or less freely and ex- 

 tensively according to circumstances. In volcanic districts, 

 where the heat may be great at comparatively small depths, 

 analogous phaenomena sometimes occur at the surface, which 

 are probably caused by the action and reaction of steam and 

 water. Amongst these may be included the intermitting 

 Geyser springs in Iceland, as well as some of the mud volca- 

 noes found in Sicily, and in Asia, and America. 



It seems probable that earthquakes may be produced by the 

 action of highly elastic vapour rapidly generated at great 

 depths, in consequence perhaps of copious and sudden in- 

 fluxes of water into intensely heated parts of the earth; and 

 their lines of direction are doubtless influenced by those of the 

 fissures or veins of the districts in which they occur. But 

 these are phasnomena of comparatively rare occurrence, and 



