RELATION OF TERTIARY MOVEMENTS TO EARTH's PLAN 221 



ments from the north pole and decrease those from the south pole. Thns 

 the pole from which the first great movement occurred would take the 

 lead in crustal movements, and would continue henceforth to be the one 

 from which the greatest movements would take place. The ocean would 

 follow the shifting center of gravity, and thus would tend to draw away 

 slightly from the north polar regions and rise slightly upon the south 

 polar regions. Both of these effects tend to a concentration of land 

 around the north pole and of water around the south pole. The stronger 

 crustal creep from the north pole appears to have carried the land away 

 from the immediate vicinity of that pole, while the feebler dispersion 

 from the south pole has left a high, extensive land-mass in that region. 



The southward tapering of the continents may also be related in some 

 way to the dominance of crustal movements from the north pole. The 

 strong dispersion from this pole and the drawing away of the water has 

 left a girdle of land near the Arctic circle which is continuous, except 

 for the narrow Bering Strait and the wider rifts on the east and west 

 sides of Greenland. Even if the entire surface of the globe north of the 

 45th parallel of north latitude had been land at the beginning of the 

 Tertiary movements, and if all the crust of this area had crept away 

 southward into latitudes lower than the 45th parallel, it could not have 

 filled the space south of this parallel with land, because of the great in- 

 crease of area. At the same time, the north polar flattening appears to 

 have been confined almost wholly to the area north of the 45th parallel. 

 Hence, in moving southward there was a diminishing power of the de- 

 forming force and at the same time a very large increase of surface area. 

 In these two circumstances there are elements which necessarily imposed 

 limitations upon the southward extension of the continents, but they 

 seem to suggest broad lobate forms like Asia and Australia, rather than 

 tapering, pointed forms like North and South America. But the Amer- 

 ican and African forms may have arisen from the influence of pre- 

 existent meridional faults or lines of weakness which drew the crustal 

 movements to one side. 



SUESS ON THE CaUSE OF DEFORMATION OF StILVND-LINES 



It does not fall within the scope of this paper to attempt any discus- 

 sion of the ultimate causes of the Tertiary mountain making, nor of the 

 more recent displacement of the strand-lines, but any suggestion by Suess 

 upon these points is worthy of the most careful consideration. Because 

 he has reviewed the field more extensively and more thoroughly than any 

 other living man, we are naturally inclined to look to him more than to 



XVI— Bull. Geol. Soc. Am.. Vol. 21. IDOO 



