48 HISTORY OF THE OCEANS 



zone and the associated Tehuantepec ridge are continued across 

 Central America and reappear in the Caribbean, but the con- 

 nection does not seem at all firmly established. Menard and 

 Fisher hav^e also suggested that fracture zones in the northeast 

 Pacific are continued in China. 



There seems to be substantial evidence that in the Atlantic 

 and the Pacific the structures of the continents and the oceans 

 are rarely directly connected. Obviously the evidence is not suf- 

 ficient to establish such a generalization, and the object in pro- 

 posing it is largely to suggest things that should be looked for. 

 Particular interest attaches to structures, such as the Cameroons 

 and the Lomonosov ridge, which may represent trends crossing the 

 continental edge. 



If the fold lines of western Europe and of Newfoundland are 

 cut off between the shore and the edge of the continental shelf, it 

 would strongly suggest that the ocean floor was not present when 

 the folding took place and would be consistent with the hypothesis 

 of continental drift. New evidence on this has come from paleo- 

 magnetism; the whole material has recently been reviewed by 

 Blackett et al. (1960), who make a strong case for relative move- 

 ments of the continents. The evidence seems strong enough to 

 justify the effort needed to obtain some independent check; a 

 continuation of Caledonian or Hercynian structures from Europe 

 well out into the Atlantic would go a long way to show that the 

 ocean had not been formed by a post- Paleozoic westward 

 movement of America. 



Paleomagnetic studies cannot detect a movement in longitude; 

 particular interest therefore attaches to any evidence that can be 

 found for east-west movements from a study of the oceans. Many 

 of the arguments that have been suggested are inconclusive. The 

 observed general similarity of crustal structure in the Atlantic and 

 Pacific is perhaps not to be expected if the Atlantic is a recently 

 opened gap. The mid-Atlantic ridge and particularly its central 

 valley might be regarded as the place where the Atlantic is at 

 present widening. The continuation of this feature round the south 

 of Africa and up the Indian Ocean to the Red Sea suggested by 

 Rothe (1954) and by Ewing and Heezen (1956) is consistent with 



