338 



SCIENCE 



[N. S. Vol. XL. No. 1027 



pole. An examination of their original papers 

 shows, however, that although they concede 

 limited wandering to have possibly taken place 

 under certain conditions, yet these conditions 

 can not be admitted as existing throughout 

 geologic time. Darwin's paper^ is most thor- 

 ough and conclusive. In it he shows that the 

 axis of rotation will follow the axis of figure. 

 That is, if profound subsidence of miles should 

 take place at some locality, say Boston, and 

 also at its antipodal point, until the connect- 

 ing line was the shortest diameter of the earth 

 and if there should simultaneously occur an 

 upheaval around a great circle at ninety de- 

 grees from this point until this circle should 

 constitute an equatorial bulge, then, and only 

 then, could Boston come to lie on the axis of 

 the earth. 



If the change took place cataclysmically and 

 the earth were sufficiently rigid, there would be 

 set up a permanent Eulerian nutation, or cir- 

 cular wobbling of the pole, but if the change 

 was slow and intermittent the Eulerian nuta- 

 tion would never be large. The lack of 

 cumulative effect would be due to the vari- 

 able positions of the instantaneous axis of 

 rotation with respect to the principal axis of 

 the earth at the times of successive impulses.' 

 Thus, as a result of movements through the 

 earth's body, shiftings of the axis of rotation 

 would take place, keeping it close to the axis of 

 figure. The axis of rotation at any time is 

 consequently stable. To change it there must 

 be shiftings of matter in order to change the 

 axis of figure. As the radii would have to 

 change in length by many miles for an exten- 

 sive migration, the mere gradational processes 

 of erosion and sedimentation could not be of 

 much effect. There would have to be internal 

 changes of form far greater than the known 

 amounts of uplift and depression. Any ex- 

 planation as to what force could cause the 



2 " On the Influence of Geological Changes on 

 the Earth's Ajxis of Rotation," Phil. Trans. Eoyal 

 Soc, Part I., Vol. 167, 1877, pp. 271-312; Vol. 

 III., Collected Works. 



3 6. H. Darwin, ' ' On Professor Haughton 's Esti- 

 mate of Geological Time," Proc. Boyal Soc, 

 XXVII., pp. 179-183, 1878, 



earth to expand in one direction and contract 

 in another direction to these great amounts is 

 absent. Apparently the earth would have to 

 be granted an amoeboid power, which Simroth 

 as the sponsor of the pendulation theory and a 

 biologist might be willing to confer. By as- 

 suming a plastic earth and convective move- 

 ments in its internal mass, energy could be 

 supplied and a considerable polar wandering 

 result, the process being analogous to a proto- 

 plasmic streaming. Lord Kelvin granted the 

 possibility of a considerable polar wandering 

 during the early plastic stage of the earth, but 

 held that practical rigidity had prevailed 

 throughout geologic history.* These state- 

 ments are sufficient to show the conflict be- 

 tween the mechanics of a revolving solid globe 

 and any hypothesis of unlimited wandering 

 through geological time. 



But movements of elevation have gone for- 

 ward in some places, of subsidence in others. 

 What maximum polar shifting could be the re- 

 sult of such continental and oceanic move- 

 ments ? Darwin has given a quantitative solu- 

 tion to this question. Taking the areas as in 

 the most favorable situation to affect the axis 

 of rotation, he assumes that one area is ele- 

 vated 10,000 feet and another equal area sub- 

 sides 10,000 feet. A table shows the relation 

 between the size of these areas and the result- 

 ing deflection of the pole. A land mass as 

 large as Africa thus favorably situated and 

 undergoing reciprocal vertical movement with 

 a section of oceanic bottom of like area, would 

 result in a deflection of the pole amounting to 

 about two degrees. If such changes were pro- 

 gressive and in the right direction Darwin 

 states that they might account for a change of 

 10° to 15° since the consolidation of the earth. 

 The kind of progressive changes which would 

 account for this amount of shifting have not, 

 however, been shown to have occurred through 

 geologic history. 



To affect the position of the pole the most 

 favorable situation is for uplift to occur at two 

 antipodal regions in latitude 45°; for depres- 

 sion to take place on the same meridian circle, 



i Trans. Geol. Soc. Glasgow, Vol. XIV., p. 312, 

 1874. 



