364 A. p. COLEMAN GI/ACIAL PERIODS AND GEOLOGICAL THEORIES 



varying eccentricity of the earth's orbit seem to be ruled out, as shown by 

 more than one writer, because of the relatively large number of rather 

 evenly distributed ice ages which they suggest, and also by the assumption 

 of alternating conditions in the two hemispheres. All the geological evi- 

 dence points toward simultaneous glaciation in the northern and southern 

 hemispheres, and the great extension of glaciers on mountains under the 

 equator is inexplicable on the theory of varying eccentricities of the 

 earth's orbit. 



On the other hand, the strange clustering of great ice-sheets about cer- 

 tain centers suggests some factor which is not universal, but local in a 

 broad way. A shifting of the poles of the earth has naturally been 

 brought forward to account for the Permo-Carboniferous ice-sheets on 

 low ground on both sides of the tropics; and this would aid in solving 

 some of the problems connected with such an ice age, but would raise 

 new diiBculties in other directions. 



If we imagine the south pole of the earth shifted to the central point 

 between the glaciated areas in South Africa, India, and Australia, it 

 would stand about in latitude 20° or 25° and longitude 75° as compared 

 with the present arrangement. The distance of the nearest glaciated 

 regions on the three continents from the supposed pole would be about 

 35°, so that their latitude would be 55° south. Under present conditions 

 this would not imply glaciation unless on ground rising much above the 

 sealevel. The glaciated points farthest away from the pole, as, for exam- 

 ple, in New South Wales, would have a latitude of about 24° south of the 

 new equator, which would make ice action impossible except on very high 

 mountains, with a zonal arrangement of climate like that at present. 



The effects on the climate due to the much greater inclination of the 

 earth's axis to the ecliptic are, however, not taken into account here. No 

 doubt the much greater difference between summer and winter and the 

 relative narrowness of the tropical belt would greatly affect climates, but 

 it would lead too far to discuss the results here. 



If the south pole stood in the middle of the Indian ocean or of a Gond- 

 wana land occupying its present position, the north pole would be in 

 northern Mexico, near the boundary of New Mexico or Texas. Glacial 

 conglomerates have not yet been reported from the Permo-Carboniferous 

 of that region, though a conglomerate suggesting ice action has been de- 

 scribed by Doctor Cross from Colorado; and it is improbable that such 

 tremendous glaciation could exist in the southern hemisphere, while re- 

 gions much nearer the north pole were not greatly refrigerated. 



A shifting of the poles would do little toward accounting for the Permo- 



