88 PHILOSOPHICAL SOCIETY OF WASHINGTON. 
in the neighborhood of, large bodies of water; 4th, volcanoes near 
the sea often deliver salts which may reasonably be supposed _ to be 
the same as those contained in the ocean; 5th, the analogy of gey- 
sers gives us a series of phenomena which seem to be, in many respects, 
quite parallel, and which have been satisfactorily explained in a 
similar way. 
To this view of the origin,and causation of voleanic activity there 
are some objections. There is difficulty in understanding how water 
obtains access to hot magmas. No doubt the rocks are full of 
fissures, but we cannot, by any means, confidently infer that these 
fissures extend sufficiently deep to afford free or even capillary pas- 
sages to melted magmas beneath. We should more legitimately 
infer that the heat increases gradually with the depth. At adepth 
of a few miles the rocks presumably have a temperature which, 
though high, is still below fusion, and at such temperatures it is well 
known that all the siliceous or rocky materials we are acquainted 
with are viscous. Remembering the immense statical pressure due 
to a thickness of a single mile of rocks, all fissures at such depths 
would be closed, as if the rocks were wax or butter. 
2d. Although the contact of cold water with intensely hot masses 
will surely produce a violent explosion, we are not at liberty to admit 
offhand that cold water does obtain such contact in the volcanoes. 
On the contrary, as it penetrates it takes up the heat of the rocks 
through which it passes. But water is believed by all physicists to 
have what is technically termed a critical temperature, i. ¢., a tem- 
perature at which it can exist only in the form of vapor however 
great the pressure, and this temperature is computed theoretically 
to be about 772° F., which is far below that of melted rock. If 
therefore, water could reach the liquid lavas below, it would reach 
them only in the form of vapor. There is indeed no difficulty in 
supposing that the vapor of water may, under great statical pres- 
sure, be forced into the rocks, passing between inter-molecular spaces. 
This is but one aspect of the phenomena of the diffusion and occlu- 
sion of gases in solids, and we know that water-vapor in large quan- 
tities is readily occluded by lava. But this is evidently no explan- 
ation of the explosive action. It isin the broadest possible con- 
trast with the gross conception of the sudden access,of cold water 
to hot bodies. The presumption is, under the process here sug- 
gested, that the vapor of water might penetrate slowly into regions 
of great heat until the hot magmas were saturated, and then the 
