EMERSON— RECURRENT TETRAHEDRAL DEFORMATIONS. 451 



arrows at equidistant points on the map, in order to make clear the 

 following explanation. 



Under the first arrow, Europe-Africa has not suffered torsion 

 and remains, as Green's map shows, closely occupying the place of 

 the original tetrahedral elevation. There has been no torsional 

 motion between Europe and Africa, because of the small size of the 

 former and the large size of the latter and the parallel relations of the 



^ ^ ^ 





Fig. I. Map showing the tetrahedral deformation. 



old and new equators. Underneath the second arrow is Australia 

 and since the whole of western Australia is unfolded Archaean this 

 meridian may represent the original and symmetrical position of the 

 second tetrahedral elevation, and its north part (Asia) being ab- 

 normally large has lagged westwardly, until in its last position it 

 coalesces with Europe. The map shows by a dotted line the de- 

 pressed area north of the Caspian — the former northward extension 

 of the Indian Ocean. 



The next arrow shows that North America is in or near its true 

 tetrahedral position, while South America has drifted eastward, due 

 to its lesser elevation and the excessive eastward thrust of the excep- 

 tionally broad South Pacific sea bottom, which was an abnormally 

 large depression from the beginning. Thus the largest elevated land 



