544 Royal Society. 



to overcome considerable resistance in its attempts to regain a state 

 of equilibrium by a movement over its fluid nucleus. 



"Whether the thickness of the earth's crust was not in early geo- 

 logical times less than at present, so as to render it more susceptible 

 of alterations in position — whether the spheroid of the fluid mineral 

 nucleus corresponds in form with the spheroid of water which gives 

 the general contour of the globe — whether or no there are eleva- 

 tions and depressions upon the nucleus corresponding to some extent 

 with the configuration of the outer crust, and whether the motion 

 of the crust upon it, besides effecting climatal changes, might not 

 also lead to some elevations and depressions of the land, and produce 

 some of the other phenomena mentioned by Sir Henry James, are 

 questions which I will leave for others to discuss. 



My object is simply to call attention to what appears to me the 

 fact, that if, as there seems reason to suppose, our globe consists of 

 a solid crust of no great thickness resting on a fluid nucleus, either 

 with or without a solid central core, and if this crust, as there is 

 abundant evidence to prove, is liable to great disturbances in its equi- 

 librium, then it of necessity follows that changes take place in the 

 position of the crust with regard to the nucleus, and an alteration 

 in the position of the axis of rotation, so far as the surface of the 

 earth is concerned, ensues. 



Without in the slightest degree undervaluing other causes which 

 may lead to climatal changes, I think that possibly we may have 

 here a vera causa such as would account for extreme variations from 

 a Tropical to an Arctic temperature at the same spot, in a simpler 

 and more satisfactory manner than any other hypothesis. 



The former existence of cold in what are now warm latitudes might, 

 and probably did in part, arise from other causes than a change in 

 the axis of rotation, but no other hypothesis can well account for 

 the existence of traces of an almost tropical vegetation within the 

 Arctic circle. 



Of the former existence of such a vegetation, the evidence, though 

 strong, is not conclusive. But if the fossil plants of Melville Island, 

 in lat. 75° N. *, which appear to agree generically with those from 

 the English coal-measures, really grew upon the spot where they were 

 now discovered, they seem to afford conclusive evidence of a change 

 in the position of the pole since the period at which they grew, as 

 such vegetation must be considered impossible in so high a latitude. 



The corals and Orthoceratites from Griffiths Island and Corn- 

 wallis Island, and the liassic Ammonites from Point Wilkie, Prince 

 Patrick's Island, tell the same story of the former existence of some- 

 thing like a subtropical climate at places at present well within the 

 Arctic circle. 



To use the words of the Rev. Samuel Haughtonf, in describing the 

 fossils collected by Sir F. L. M c Clintock, "The discovery of such 

 fossils in situ, in 76° N. latitude, is calculated to throw consider- 

 able doubt upon the theories of climate, which would account for 

 all past changes of temperature by changes in the relative position 

 * Lyell, ' Principles of Geology,' 1853, p. 88. 

 t Journal of the Eoyal Dublin Society, vol. i. p. 244. 





