392 Dr. James Croll — On Geological Time. 



changes of geological climate on tlie hypothesis of a change in the 

 axis of rotation. This conclusion has been further borne out by 

 another mathematician, the Eev. E. Hill, in an article in the June 

 Number of the Geological Magazine. And Professor Haughton, 

 in a paper read before the Eoyal Society, April 4th, and published in 

 JVafwre, July 4th, entitled, "A Geological Proof that the Changes 

 of Climate in Past Times were not due to Changes in the Position of 

 the Pole," has proved from geological evidence that the Pole has 

 never shifted its position to any great extent. " If we examine," he 

 says, " the localities of the fossil remains of the Arctic regions, and 

 consider carefully their relations to the position of the present North 

 Pole, we find that we can demonstrate that the Pole has not sensibly 

 changed its place during geological periods, and that the hypothesis 

 of a shifting pole (even if permitted by mechanical considerations) 

 is inadmissible to account for changes in geological climates." 



There is no geological evidence to show that, at least since Silurian 

 times, the Atlantic and Pacific were ever in their broad features 

 otherwise than they are now — two immense oceans separated by 

 the Eastern and Western continents — and there is not the shadow 

 of a reason to conclude that the poles have ever shifted much from 

 their present position. On this point I cannot do better than quote 

 the opinion recently expressed by Sir William Thomson : • 



"As to changes of the earth's axis, I need not repeat the statement 

 of dynamical principles which I gave with experimental illustrations 

 to the Society three years ago ; but may remind you of the chief 

 result, which is that, for steady rotation, the axis round which the 

 earth revolves must be a ' principal axis of inertia,' that is to say, 

 such an axis that the centrifugal forces called into play by the 

 rotation balance one another. The vast transpositions of matter at 

 the earth's surface, or else distortions of the whole solid mass, which 

 must have taken place to alter the axis sufficiently to produce sensible 

 changes of the climate in any region, must be considered and shown 

 to be possible or probable before any hypothesis accounting for 

 changes of climate by alterations of the axis can be admitted. This 

 question has been exhaustively dealt with by Mr. George Darwin 

 in a paper recently communicated to the Eoyal Society of London, 

 and the requisitions of dynamical mathematics for an alteration of 

 even as much as two or three degrees in the earth's axis in what may 

 be practically called geological time shown to be on purely geological 

 grounds exceedingly improbable. But even suppose such a change 

 as would bring ten or twenty degrees of more indulgent sky to the 

 American Arctic Archipelago; it would bring Nova Zembla and 

 Siberia by so much nearer to the pole : and it seems that there is 

 probably as much need of accounting for a warm climate on one side 

 as on the other side of the pole.' There is in fact no evidence in 

 geological climate throughout those parts of the world which geo- 

 logical investigation has reached, to give any indication of the poles 

 having been anywhere but where they are at any period of geological 

 time." ^ 



' This has been proved to be the case by Prof. Haughton, Nature, July i, 1878. 



2 Trans, of Geol. Soc. of Glasgow, Feb. 22, 1877. 



