14 Windhausen — The Cretaceous- Tertiary 



tlu> final stage in the formation of the Atlantic basin was 

 reached. The great meridional lines of its present forms 

 were here definitely fixed. ;is That the Parana Formation 

 does not agree in faunistic character with the older trans- 

 gressions, cannot be surprising ; it is an Atlantic forma- 

 tion in every respect. 



In the light of these facts, the fauna of the San Jorge 

 loses all strangeness of character. The assumption of 

 Burckhardt that this fauna was more or less similar to 

 that of the Upper Cretaceous strata of the Brazilian 

 coast (Maria Farinha near Pernambuco) was not sup- 

 ported by v. Ihering's studies. 30 It is improbable that 

 a direct connection existed between the San Jorge-trans- 

 gression and the Brazilian province. Any movement or 

 migration of this period must have followed along the 

 old route of marine wanderings along the westcoast and 

 across the Isthmus of Panama and the region of the 

 Caribbean Sea. Even if greater knowledge and further 

 comparison of faunas should indicate genetic connections 

 with the North African province, the exchange of marine 

 faunas must have taken place along this same route. 

 The assumption of a direct Atlantic connection does not 

 agree with the known facts. 



Perhaps future collections of fossils and critical com- 

 parisons of the San Jorge will prove a certain prepon- 

 derance of relationship to the Australian and New 



elements, and a strong similarity is noted with living types of the Pacific 

 fauna. This may be regarded as evidence that the Centro-American land- 

 bridge became steady approximately in Miocene time, whereas before there 

 existed a free circulation between the South American westcoast and the 

 Atlantic north of the Equator. Special currents might favor a prepon- 

 derance of Atlantic elements in the Navidad Beds. — According to Donald F. 

 Macdonald the landbridge of Panama appeared for the first time in the 

 Oligocene; but until the present there has been a change of submergences 

 and upliftings. At all events, it can be proved that, beginning approxi- 

 mately with the close of the Miocene, the existence of a threshold is 

 strongly marked by the above changes of marine faunas on the South 

 American westcoast. 



38 According to De Geer, the continent that occupied the northern portion 

 of the Atlantic was submerged in the Neogene, opening the way for the 

 waters of the Arctic Ocean to the Atlantic basin. It may be, that this 

 phenomenon is parallel and contemporaneous to the alluded occurrences in 

 the Atlantic of the southern hemisphere. See De Geer, Kontinentale 

 Niveauveranderungen im Norden Europas, Compte rendu, Congres Geolo- 

 gique Internationale, pp. 849 etc., Stockholm, 1910. 



89 For instance Cardita morganiana Eathb. has been cited very fre- 

 quently as a proof of correlations between the Upper Cretaceous deposits 

 of Brazil and Argentine; but v. Ihering has shown that the Cardita of 

 the Eoca Beds cannot be compared with the alluded Cardita morganiana. 



