504 ON THE SUCCESSIVE FORMS 



isting or recently extinct volcanoes. And thus is every 

 thing that can be demanded in proof of the assigned 

 causes of these revolutions, demonstrated by the 

 clearest evidence. The theory is perfect, even to its 

 details and to those of each individual action. 



I must not however quit this subject, without no- 

 ticing a theory which supposes abysses within the 

 earth, and subsidences of the strata into these ; espe- 

 cially as I have pointed ofit what the fabricators of this 

 hypothesis never had shown, the demonstrated subsi- 

 dence of portions of the surface, in antient times, as 

 similar phenomena now occur, in a partial manner, 

 in volcanic countries. With them, it was pure hy- 

 pothesis without a fact in support. The appearances 

 proving elevation are so universal and decisive, that 

 this needs not be insisted on. There could not be an 

 abyss in a fluid mass ; and if the earth be therefore 

 such, whatever cavities it may contain must be in its 

 solid parts, and thence, comparatively superficial ; as 

 its high specific gravity also shows that such cavities 

 cannot be extensive, should they exist ; and as we 

 cannot even easily conceive a cavity under the actual 

 or neighbouring presence of a fluid. And I have also 

 shown how these depressions might take place through 

 a mere change of relative level, without the necessity 

 of any such supposition. Yet there are indications 

 of a peculiar structure in the earth which might be 

 called cavernous, if we allow that these are filled by 

 a fluid ; as they are otherwise not conceivable. These 

 are, the linear directions of volcanoes, and the singu- 

 larly linear tendencies of the elevated edges of strata. 

 On the nature of this disposition it seems to me, how- 

 ever, in vain to speculate ; and I willingly therefore 

 leave it to the researches and reasonings of future geo- 

 logists. I can conceive it to have been produced by 

 former displacements of solid strata : but that is all. 



