27 



short, no cooling power at all is needed further than that of con- 

 duction and radiation from the surface of the bar, because of the 

 extreme feebleness with which heat passes through its interior 

 parts. What is the difficulty of applying this reasoning to the 

 stony crust of the earth ? " It is simply this, that heat is kept 

 up by combustion, and that must be supplied with oxygen. 

 Consequently that part exposed to the fire must necessarily con- 

 sume and would finally decompose. Therefore a crust floating 

 on an incandescent element under similar circumstances, as above 

 described, could not increase, but would necessarily dissolve. 

 The above bar should be placed on the fire sideways, to repre- 

 sent the assumed condition of the crust. 



Such a doctrine deserves no serious attention, when we find 

 that the observed phenomena are consistent with those pro- 

 duced by chemical actions. If we admit the existence of sub- 

 terranean currents, and that these exert a slow decomposing 

 power, like that of the voltaic battery, we have a sufficient power 

 for our purpose. In the first place, we have a mechanical ten- 

 sion on the consolidated parts of the rocks, by the linear action of 

 the currents passing through them ; and should the intensity of 

 the currents be very great, fractures would ensue, more or less 

 at right angles to the direction of the force. These fractures 

 would admit air and water, and thus produce intense heat, by 

 the avidity with which the metallic nature of the bases of the 

 earths and alkalies combines with the oxygen. 



That nearly all the substances which constitute the crust of 

 the globe are found in solution as well as solid, saturated through- 

 out the rocks, and to such a degree sometimes as to issue out 

 and form springs, is well known ; therefore, judging from the 

 violent effects on a small scale which we are able to produce 

 by experiments, a heat would be engendered quite adequate to 

 occasion all that takes place in volcanic eruptions. It is a fact, 

 that nearly all active volcanic groups are within a short distance 

 of the sea ; and even those that are situated at a distance from 

 it may be connected with subterraneous channels of water. It is 

 also a well-known fact in South America that fish are commonly 

 thrown out of the crater, and some of the eruptions consist en- 

 tirely of mud or muddy water, thus giving a still greater proof 

 of their origin. The sudden fracture, as well as the sudden 

 expansion of the gases, would produce a vibratory jar, which, 



