Natural History of Volcanos and Earthquakes. 279 



were produced by forces which were in operation for a very short 

 period only. Changes in the contiguous rocks, and the imbed- 

 ment of fragments of them in the volcanic rocks, render it also 

 equally probable that these masses were raised in a fluid, or at 

 least softened state, and either rose above the surface of the earth 

 in the form of conical mountains, or remained adhering in rents 

 of the rocks. These phenomena, then, belong entirely to the 

 same class as the elevations of lava in volcanic craters. When, 

 on the other hand, no changes are perceived in the contiguous 

 rocks, when these have been simply broken through and upraised, 

 when the broken masses consist of acute-angled fragments of all 

 dimensions heaped one upon another, then we cannot assume 

 that the elevations took place in a fluid or softened state. 



Were elevations of this kind the work of a short space of time, 

 or did they proceed slowly ? In vain do we look around us for 

 some clew to the solution of this question. From physical 

 grounds we are led to the followmg conclusions. If fused rock 

 come in contact with water in the interior of the earth, the wa- 

 tery vapor disengaged, will operate, with the whole expansive 

 force which it can acquire from the heat of the rock, in a short 

 time ; provided that the continued formation of vapor be not lim- 

 ited by want of water. It is the same process as that which 

 takes place in the glass-blower's blow-pipe when he forms large 

 globes. If, then, water acts on fused masses in a confiined space, 

 we have the conditions requisite for producing a rapid elevation, 

 and therefore, as a general rule, we may regard elevations of fused 

 masses and rapid elevations as co-ordinate phenomena. If, on the 

 other hand, we imagine a solid rock deep under the surface, 

 whose temperature is far below a red heat, then its elevation 

 can take place only when a considerable source of heat exists un- 

 der the rock, which gives rise to the formation of vapor. But 

 the more the heat of the vapor exceeds that of the rock, which is 

 to be raised and supported by it,-the more will it become conden- 

 sed, and thus a great part of the eflfect is lost. If the condensed 

 vapor return to the source of heat, it will again assume the form 

 of vapor, and thus a constant circulation will ensue. It is actu- 

 ally a process of heating by steam. If the solid rock be a very 

 bad conductor of heat, then that surface which is in contact with 

 the vapor, may gradually acquire its temperature, and the vapor 

 thus attain its maximum of operative force. It naturally depends 



