bearing on theoretical Speculations. 361 



periods ; the only question, I must confess, appears to me to be, 

 whether we prefer embracing an adequate or an inadequate cause. 

 In like manner as to volcanic agency, we are both of us 

 equally ignorant as to the cause of this power; but surely 

 whatever that cause may be, there can be nothing unphiloso- 

 phical in supposing that it might have been capable of acting 

 with greater energy, when the materials constituting the crust 

 of the earth were only beginning to be deposited, than at 

 present, when the whole weight and resistance of the actual 

 solid crust opposes it. Whatever were the muscular power of 

 Atlas, he was probably capable of more violent exertion 

 in his unfettered state, than he was after Jupiter had buried 

 his limbs beneath the mass of iEtna, the " column of the 

 heaven." 



I shall now, then, enter on my proposed examination of 

 those phaenomena of geology which seem to bear most directly 

 on theoretical speculations, stating each as shortly as possible, 

 and then appending (under each article) the observations 

 which it appears to me to suggest. 



I. The phenomenon which may claim our earliest atten- 

 tion is the general form of the terraqueous globe as a sphe- 

 roid of rotation. This undoubtedly appears to indicate, that, 

 at the time when it assumed that figure, the mass must have 

 been (at least in great measure) in a fluid state. 



Observations. — If so, there will remain before us only the 

 following possible alternative; at present, either the globe does, 

 or it does not, retain this original fluidity. I will say a few 

 words on either branch of this alternative. 



If it shall be considered as most probable that the globe 

 has now lost the fluidity which once pervaded a sufficient 

 portion of its mass to account for this figure, the whole 

 argument must surely at once be conceded in favour of those 

 geologists who maintain that the causes which produced the 

 geological convulsions acted under circumstances essentially 

 different from the present; for nothing can well be more dif- 

 ferent than a fluid and a solid globe. 



But it may be maintained, on the other hand, that the flu- 

 idity of the central mass still remains, on which the crust of 

 the surface floats; and it may be argued that the extensive 

 oscillations of earthquakes, often affecting such vast portions 

 of the surface, afford countenance to this idea. On this sup- 

 position we may inquire whether this fluidity be igneous, or 

 aqueous; but that it cannot be the latter, the ascertained spe- 

 cific gravity of the planet seems to demonstrate : allow it then 

 [argumenti causa) to be igneous; we shall thus have a central 

 nucleus in a state of igneous fluidity, which has been gradually 



N. S. Vol. 8. No. 47. Nov. 1830. ' 3 A covered 



