212 WAKREN UPHAM, ESQ., ON CAUSES CF THE ICE AGE. 



large areas besides the Quateniary and Paleozoic ice ages, 

 which were divided probably by ten or fifteen million 

 years. 



21 The only remaining theory dependent on the earth's astro- 

 nomic relationship which we need to examine is the suggestion 

 first made in 18()(> by Sir J(4in Evans,* that, while the 

 earth's axis probably remained nnchanged in its direction, 

 a comparatively thin crust of the earth may have gradually 

 slipped as a whole npon the much larger nnclealmass so that 

 the locations of the poles upon the crust have been changed, 

 and that the Glacial period may have been due to such a 

 slipping or transfer by which the regions that became ice- 

 covered were brought very near to the poles. The same or 

 a very similar view has been recently advocated by Dr. 

 Fridtjof Nansen, who writes : " The easiest method of explain- 

 ing a glacial epoch, as well as the occurrence of warmer 

 climates in one latitude or another, is to imagine a slight 

 change in the geographical position of the earth's axis. Jf, 

 for instance, we could move the North Pole down to some 

 point near the west coast of Gi'eenland between 6U° and t>o° 

 N,L., we could, no doubt, produce a glacial period both in 

 Europe and America."! 



22 Very small changes of latitude which had been detected 

 at astronomical observatories in England, Germany, Piussia, 

 and the United States, seemed to give some foundation tor 

 this theory, which in 1891 was regarded by a few American 

 glacialists as worthy of attention and of special investiga- 

 tion by astronomers, with temporary establishment of new 

 observatories for this purpose on a longitude about lb<'° 

 from Greenwich or from Washington. During the year 

 189^, however, the brilliant discoveries by Dr. 8. C. Chandler* 

 of the periods and amounts of the observed variations of 

 latitude, showing them to be in two cycles respectively of 

 twelve and fourteen months, Avith no appreciable secular 

 change, forbid reliance on this condition as a cause, or even 

 as an element among the causes, of tlie Ice age. This 

 theory is now entirely out of the field. Sir Robert S. Ball, 

 after revicAving Dr. Chandler's investigations, estimates that 



^ On a por,sihle Geological Cause of Changes in tlie Position of the Axis 

 oj the Earth's Crust, Proceedings of tlie Royal Society of London, vol. xv, 

 ])].. 46-54, Feb. 28, 1866. 



t The First Crossing of Oreenland (1890), vol. ii, p. 454. 



+ Astronomical .Joxirnal (Boston, Mass.), vol. xii, ])p. 57-62, 65-72, and 

 97-101, Aiig. 4 and 23, and Nov. 4, 1892. 



