524 eepoet— 1878. 



described seems entirely out of place in a district within six hundred miles of the 

 pole, to which indeed, if land then extended so far, these Arctic forests must have 

 also extended in Miocene times. Making all allowance for the possibility of the 

 habits of such plants being so changed that they could subsist without sunlight 

 during six months of a winter of even longer duration, I cannot see how so high a 

 temperature as that which appears necessary, especially for the evergreen varieties, 

 could have been maintained, assuming that Grinnell Land was then as close to the 

 North Pole as it is at the present day. Nor is this difficulty decreased when we 

 look back to formations earlier than the Miocene, for the flora of the secondary and 

 Palaeozoic rocks of the Arctic regions is identical in character with that of the 

 same rocks when occurring twenty or thirty degrees farther south, while the corals, 

 encrinites, and cephalopods of the carboniferous limestone are such as, from all 

 analogy, might be supposed to indicate a warm climate. 



The general opinion of physicists as to the possibility of a change in the posi- 

 tion of the earth's axis has recently undergone" modifications somewhat analogous 

 in character to those which, in the opinion of some geologists, the position of the 

 axis has itself undergone. Instead of a fixed dogma as to the impossibility of 

 change, we find a divergence of mathematical opinion and variations of the pole 

 differing in extent, allowed by different mathematicians who have of late gone into 

 the question, as for instance the Rev. J. F. Twisden,* Mr. George Darwin,t Pro- 

 fessor Haughton,} the Rev. E. Hill,§ and Sir William Thomson.|! All agree in the 

 theoretical possibility of a change in the geographical position of the earth's axis 

 of rotation being affected by a redistribution of matter on the surface, but they do 

 not appear to be all in accord as to the extent of such changes. Mr. Twisden, for 

 instance, arrives at the conclusion that the elevation of a belt twenty degrees in 

 width, such as th^it which I suggested in my presidential address to the Geological 

 Society in 1870, would displace the axis by about ten miles only ; while Professor 

 Haughton maintains that the elevation of two such continents as Europe and Asia 

 would displace it by about sixty-nine miles ; and Sir W. Thomson has not only ad- 

 mitted, but asserted as highly probable, that the poles may have been in ancient 

 times " very far from their present geographical position, and may have gradually 

 shifted through ten, twenty, thirty, forty, or more degrees without at any time any 

 perceptible sudden disturbance of either land or water." 



I am glad to think that this question, to which I to some extent assisted to 

 direct attention, has been so fully discussed, but I can hardly regard its discussion 

 as being now finally closed. It appears to me doubtful whether eventually it will 

 be found possible to concede to this globe that amount of solidity and rigidity 

 which at present it is held to possess, and which to my mind at all events seems to 

 be in entire disaccordance with many geological phenomena. Yet this, as the 

 Rev. 0. Fisher ^[ has remarked, is presupposed in all the numerical calculations 

 which have been made. I am also doubtful whether, in the calculations which 

 have been made, sufficient regard has been shown to the fact that a great part of 

 the exterior of our spheroidal globe consists of fluid which, though of course 

 connected with the more solid part of the globe by gravity, is readily capable of 

 readjusting itself upon its surface, and may, to a great extent, be left out of the 

 account in considering what changes might arise from the disturbance of the 

 equilibrium of the irregular spherical or spheroidal body which it partially covers. 

 It appears to me also possible that some disturbances of equilibrium may take place 

 in a mysterious manner by the redistribution of matter or otherwise in the interior 

 of the globe. Captain F. J. Evans,** arguing from the changes now going on in 

 terrestrial magnetism, has suggested the possibility of some secular changes being 

 due to internal, and not to external causes ; and if it be really true that there is a 

 difference between the longest and shortest equatorial radii of the earth, amount- 

 ing to six thousand three hundred and seventy-eight feet,tt such a fact would appear 



* Quart. Jour. Geol. Soc, 1878, p. 35. 



f Proc. R. S., vol. xxv. p. 328. Phil. Trans., clxvii. p. 271. 



| Proc. R. S., 1877, 1878. § ' Geol. Mag.,' June, 1878. 



|| Rep. Brit. Assoc, 1876, p. 11. f < Geol. Mag.,' July, 1878. 



** Nature, May 16, 1878. ft Thomson and Tait, Phil. p. 648. 



