ON THE THEORIES OP ELEVATION AND EARTHQUAKES. 39 
with reference to such volcanos as Stromboli and Kirauea, in which the per¬ 
manent position of the surface of their fluid masses are known to be, on 
the contrary, at a great height above the level of the ocean. Still the vol¬ 
canic process is in constant and vigorous action in these volcanos, as mani¬ 
fested by their state of incessant ebullition. That this process can be main¬ 
lined by the agency above described appears to me, as far as I comprehend 
it, to involve nothing less than a mechanical impossibility. If there wero 
any free channels passing through the solid rocks which constitute the 
walls of the volcanic cavities, and communicating with the eatili’j surface 
at any point so low as the surface of the ocean, fluid lava must ineritablr be 
forced through them in an unceasing and rapid stream, leaving uu possibility 
of the descent of water through the tame chimneU. If the Insures were too 
small to form perfectly free communications with the suriace, the lava would 
still be forced into them by the enormaus hydrostatic pressure to which the 
volcanic fluid would be subjected at the depth supposed. lu this case there¬ 
fore, as well as in the former, the access of water to the lower portions of the 
fluid lava appears to he lucehanically impossible. The adrabwiDii of atmo¬ 
spheric air to these lower volcanic regioas is still more incoinfivable than 
that of water. Unless this difficulty can be explained more effectively than 
it has yet been explained, I do not understand how the tlieory involving it 
can be deemed admissible, whatever may be the arguments founded on che¬ 
mical views by which it may be .supported. 
9. M.Bischqff s I henry of Volcunxc Action. —Ati expiunation of the action 
of volcanos was proposed a few years ago by M. Bischoffof Bonn, founded 
on the hypothesis tlmt the thickness of the earrh’s solid crust docs not exceed 
twenty or thirty miles*. According to this theory, volcanic cru|tiloiis are 
aueto a column of water admitted through the .solid crust, its upper extremity 
communicating with the sea or some other permanent supply of water, and 
Its lower extremity with tho general incundescent fluid mass beneath. He 
* lows the possibility of a column of water preserving its II(|oid form, though 
extending to a depth at which the temperature umst, acconlmg to the ob- 
served law of terrestrial temperature, be much greater than that of ebullition 
under the ordinary pressure of the ntraospbere. Recent observations on the 
emperature of the (Ksysers show that the temperature of ebullition in a ver¬ 
tical column of water in those snrings increases, in consequenoe of Ibo increase 
0 pressure, much more rapidly than the terrestrial temperature increases 
generally with the depth below the surface. Still we are entirely ignorant 
ot the limits beyond which the same law of increase in the temperature of 
ebullition wiih the hioreaae of pressure might, and jirobahly would, entirely 
tail. ^ Admitting, however, the poisible existence of a column of water of the 
required length, if there were a canal free to receive it, the theory appears to 
nw to involve an insuperable mechanical difficulty of the same nature as that 
above explained in the chemical theorj*. The lower extremity of the column 
IS supposed to be converted into steam, and the steam so formetl it supposed 
capable of finding accoas beneath the solid crust to another canal terminating 
near the same point, and forming a volcauio vent, up which the fluid lava is 
sujyiaied to be impelled by the plastic force of the steam, with sufficient 
violence to produce an external eruption. Now if the internal fluid had no 
tendency in its state of repose to rise through any open channel to a jiuint higher 
than the average level of the lower .surface of the solid crust, this rxjilanation, 
though still open to objections, might not be deemed altogether inadmissible 
on mechanical grounds. But there is the strongest reason to believe that, on 
* Edinburgh New Philosophical Journal, 1838-39, p. 25. 
