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 
tocks, 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 
at the elevations took place in a fluid or softened state. 
Were elevations of this kind the work of a short space of time, 
ordid they proceed slowly? In vain do we look around us for 
some clew to the solution of this question.. From physical 
stounds we are led to the following 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 
lakes place in the glass-blower’s blow-pipe when he forms large 
globes, If, then, water acts on fused masses in a confined space, 
We have the conditions requisite for producing a rapid elevation, 
and therefore, asa general rule, we may regard elevations of fused 
ihasses 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 
fan 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 
0 be raised and supported by it, the more will it become conden- 
Sed, and thus a great part of the effect is lost. If the condensed 
Yapor return to the source of heat, it will again assume the form 
Vapor, and thus a constant circulation will ensue. It is actu- 
Ya process of heating by steam. If the solid rock be a very 
bad conductor of heat, then that surface which is in contact with 
' Vapor, may gradually acquire its temperature, and the vapor 
thus attain its maximum of operative force. It naturally depends 
