SHIFTING OF THE SOUTHERN CONTINENTS 75 



and Appalachians, Urals, and Kamchatka corresponding to the three 

 polar edges of the tetrahedron. 



SHIFTING OF THE SOUTHERN CONTINENTS 



We have, secondly, to consider the apparent eastward shifting of the 

 southern masses, which Dana enumerates among the unsolved problems 

 of geology. While Africa and Europe form a triangular mass agreeing 

 fairly in position and shape with the required tetrahedral continent, 

 South America and Australia are displaced to the east of their expected 

 position south of their northern components. 



Green explains this by saying the southern hemisphere mainly sunk 

 below the average level into a circle of lesser radius would move east- 

 wardly in advance of the rest of the earth. 



It is, indeed, suggestive that in the northern hemisphere the larger the 

 continent the greater the apparent westward motion from the position 

 required by the hypothesis; in the southern, the smaller the continent 

 the greater the eastward motion, as if in the north the elevated lands 

 had done the work, in the south the depressed seabottom. 



Since, however, Africa is scarcely shifted eastwardly in relation to 

 Europe, South America much shifted, and Australia more, no torsion of 

 the whole southern hemisphere can have brought these continents into 

 their present position. This was also recognized by Green, who said the 

 separate oceans, sinking on the west of the continents, would thrust them 

 eastwardly proportionately to the size of the oceans. 



Nor can this effect be produced "in the incipient stage of the first 

 formed crust," as Dana interprets Green, for a thick crust of effective 

 rigidity must be formed before elevations and depressions could result of 

 sufficient magnitude to be the cause of torsion between the hemispheres 

 or continental masses. 



While rejecting such torsion or moving of the continents, we may yet 

 observe that America and Asia have moved westward in another way, 

 to wit, by the sinking of lands along their eastern border and by the 

 addition of lands along their western -border, and Australia has moved 

 eastward in the same manner. 



Along New England and north rias coasts abound where mountain 

 ridges strike to the shore, showing that their continuation is to be found 

 sunken beneath the waters. 



The eastern lands from which the Appalachians derived their sedi- 

 ments are submerged. There are no post Paleozoic additions to the 

 coast north of Long island. 



On the other hand, the continent has grown westwardly by the upris- 

 ing of successive mountain chains from a line not far west of the present 



