THEORY OF VOLCANIC ENEKGY. 471 



face, but all the interior surfaces of equal density follow a similar 

 law, as is proved by the results of geodesy. Hence it follows that 

 the earth must have been in a yielding condition at a time since 

 which its velocity of rotation has been what it is now. But the 

 phenomena of mountains show that there has been considerable 

 contraction within geological periods*, which must have sensibly 

 affected the rotation. The capability of yielding must therefore have 

 continued up to a period comparatively recent ; and if so, it seems 

 most probable that it continues still ; for the only change we can 

 conceive would arise from refrigeration ; and, with all the arguments 

 we possess for a high interior temperature, it is very difficult to 

 conceive that rigidity can be due to mere cooling. 



Again, geological facts as regards climate appear to point to a 

 change in the axis of rotation. But the equatorial protuberance 

 corresponds to the present axis of rotation. A yielding condition, 

 therefore, must have extended to Miocene times at least, and there- 

 fore probably to the present. That the globe should be bodily 

 turned, or canted, over, as Mr. Belt supposes, is most improbable, if 

 not impossible. 



The idea of fiery lakes finds much disfavour with Mr. Mallet. I 

 likewise mentioned some arguments against them in my paper on 

 the elevation of mountains in 1868. Prof. Dana, whose authority 

 is great, however, appears still to regard the idea with favour. But, 

 for my own part, I must agree with Mr. Mallet. 



For many sections forward from this point I am disposed to agree 

 with Mr. Mallet's reasoning; and, indeed, to disagree with him upon 

 questions that depend upon the laws of chemistry would be very 

 presumptuous on my part. But, arriving at § 52, it seems that 

 some important objections may be raised. We here meet with the 

 author's views upon the formation of oceanic and continental areas. 



Now I cannot at present offer any explanation of these grand 

 features of the earth's surface. But, at the same time, any proposed 

 explanation of them which is not the true one will, if not refuted, 

 probably hinder a better one being sought. I shall be glad to hear, 

 therefore, what geologists in general think of Mr. Mallet's opinion, 

 which is also shared by Dana, that the oceanic and continental areas 

 have, on the whole, occupied nearly the same positions on the globe 

 at all periods from the very first. Certainly the marine origin of 

 nearly all strata seems to point to an opposite conclusion ; while the 

 need of terrestrial conditions for furnishing the detritus to form the 

 rocks which now constitute lands seems to me to require former 

 continental conditions where the ocean now rolls. Notably around 

 such an island as New Zealand there must have been much more 

 land than at present to have furnished a series of formations extend- 

 ing from the Palaeozoic to the Tertiary. 



If it be not the case that these wide features of the globe have 

 existed nearly in their present positions from the first formation of 



* See a paper by the author "On the Inequalities of the Earth's Surface 

 viewed in connexion with the Secular Cooling," Camb. Phil. Trans, vol. xii 

 pt. 2, p. 18. 



