THE GASES IN ROCKS 501 
not to bea space, if of a few inches only, at an intermediate temperature. 
It is also to be remembered that the latent heat of steam diminishes 
with the pressure until, at the critical point, it becomes zero. The 
testimony of the country rocks through which a volcanic conduit has 
passed is that metamorphism has usually progressed to some distance 
from the contact of igneous intrusion. In a long-established volcano, 
where the rocks surrounding the conduit have been heated to high 
temperatures, the deposition of the solutes from any penetrating water 
should have sealed the capillary tubes and fissures at a distance from 
the lava such that the latter cannot absorb them and keep the water- 
way open. Kemp has stated in a recent paper’ that at the contacts 
with eruptives, limestone rocks, instead of being porous, are prevailingly 
dense and compact, and often very hard to drill, as if due to deposition 
within their interstices. However, the author assigned this supposed 
deposition to magmatic waters from the intrusion. ‘This brings up a 
widely established view that magmas, instead of absorbing water from 
the intruded rocks, give it off, depositing matter in solution to form 
veins in the zone of fracture. 
To quote Van Hise:? 
In the belt of cementation, in consequence of the porosity of that zone, the 
material of the magma, both by direct injection and by transmission through water, 
may profoundly affect the average chemical composition of the intruded rock for 
great distances from the intrusive mass. 
Geikie cites a case in Bohemia, where certain Senonian marls, 
invaded by a mass of Tertiary dolerite, begin to get darker in color 
and harder in texture at a distance of 800 meters from the contact, 
while, as the intrusive mass is approached, the interstratified beds of 
sandstone have been indurated to the compactness of quartzite. 
But considering only meteoric waters at depths greater than 6,900 
feet, where water remains liquid up to the critical temperature, it is 
less probable that the pore spaces will be filled up in this manner. 
Nor does it seem likely that Daubrée’s theory that water may pene- 
trate rocks against a steam-pressure can operate at these depths, 
1 Kemp, Economic Geol., Vol. II, p. 11. 
2 Van Hise, Monograph 47, U.S. Geol. Surv., p. 714. 
3 Hibsch, cited by Geikie, Textbook of Geology, Vol. I, p. 774. 
