432 Scientific Intelligence. 
pressure of water, would, of course, be still greater. However this 
may be, it would seem that, under any probable circumstances, in re- 
gard to the ratio of increase in the earth’s temperature, the increase in 
the pressure of the lengthened column of water would not keep pace 
with the rapidly increasing tendency of the water in descending into 
more heated parts of the earth to expand into steam, the elasticity of 
which, at very high temperatures, when confined and in contact with 
water, is greatly augmented by very small increments of sensible heat. 
o water could long-remain unchanged into steam below the line of 
division between them, and there the steam would be denser than at 
any deeper station, for it would be continually diminishing in density, 
in descending further from the augmentation of the temperature of the 
earth; because the expanding 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, doubt- 
less, conform in some degree to the inequalities of the surface. It may 
be difficult, at first, to conceive the steam capable of supporting the wa- 
‘ter, or rather of existing permanently 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 alter- 
nately encroach beyond the line of demarcation; but as the checks on 
both would increase in proportion to the extent of their encroachments, 
from the diminution of the temperature above, and its augmentation 
below, such encroachments would probably not be very extensive or of 
long duration under ordinary circumstances. Suppose a temporary en- 
croachment of the water on the limits of the steam to occur at one 
point; the steam would probably encroach on the water at another at 
the same time, and then reactions taking place, the effects would be re- — 
versed. 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 motion and 
activity to the water in the neighboring fissures, causing it to circulate 
in the earth more or less freely and extensively according to cireum- 
stances. In volcanic districts, where the heat may be great at compara 
tively small depths, analogous phenomena sometimes occur at the suf- 
face, 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 volcanoes found in Sicily, and» 
in Asia and America. 
ora 
