90 PRINCIPLES OF STRATIGRAPHY 



pura lapillus, Littorina littorea, Buccinum undatum, etc., most of 

 which stilt exist in arctic and subarctic regions. 



The mammals of North America have furnished some evidence 

 of the change in climate (Hay-43). Along the cold margin of the 

 ice sheet ranged the northern Rangifcr, BodtJicriiiiii and Syinbos, 

 as shown by their remains. The giant beaver Castcroidcs lived with 

 the now extinct horses, tapirs, mastodons, elephants, mylodon, and 

 magalonyx in the southern States and continued there during the 

 Pleistocenic period. It moved northward after the melting of the 

 ice. The peccaries, apparently always lovers of a mild if not warm 

 climate, now range from Arkansas to Patagonia. In the Pliocenic 

 a species lived in Texas, while after the melting of the ice repre- 

 sentatives of the family moved northward, their remains having 

 been found in three localities upon the Wisconsin drift sheet, viz. : 

 northern Indiana ; near Columbus, Ohio, and at Rochester, New 

 York. The hairy mammoth, Elcphas primogenius, seems to have 

 always lived near the margin of the ice sheet, but the Columbian 

 elephant, E. columhi, was a denizen of warmer climates, yet its 

 remains have also been found in deposits overlying the Wisconsin 

 drift. The same is true of the mastodon, 71/. americanus, a denizen 

 of mild climates, which has not only left its remains over the south- 

 ern States, but which roamed northward during the warm post- 

 glacial period. Tlie mammals also indicate a period of warmer cli- 

 mate, during which they ranged farther north than at present, which 

 is a period of somewhat lower temperatures. This reduction, while 

 fatal to many forms, was the cause of the survivors moving south- 

 ward again. 



DiSPLACEIVJENT OF THE EaRTh's AxIS AS A CaUSE OF 



Climatic Changes. 



That a change in the position of the earth's axis would bring 

 about a change in climate, cannot be questioned, and this explanation 

 has been suggested for the glacial conditions in Pleistocenic time. 

 Davis (25) has outlined the climatic consequences of displacing the 

 poles in such a way that the north pole would be located at Iceland, 

 in latitude 70° N. on the meridian of 20° W., the following being 

 some of the effects : "First, a rearrangement of shore lines in con- 

 sequence of the adoption of new locations of polar flattening and 

 equatorial bulging. . . . Second, alteration in the paths of ocean 

 currents, of which one of the most important would be the dimi- 

 nution of the volume of warm water transferred from the southern 

 to the northern hemisphere by the oblique cross-equator current of 



