GEOLOGY OF SOUTH AMERICA 341 



Several other writers have discussed the theory of former 

 land bridges between South America and Africa and between 

 South America and other continents without dealing with the 

 geological history of South America itself. Their views will 

 be presented later on. 



The only author who, to my knowledge, has treated the 

 subject under review from a purely palaeontological stand- 

 point is Dr. Ameghino. His views were brought for- 

 ward in several important technical papers. As they may 

 have undergone slight modification in the course of time, I 

 prefer to quote his opinions from a recent semi-popular 

 account. It may be mentioned that Dr. Ameghino's * 

 theories are founded on the known distribution of fossil 

 mammals. North of the Equator, he says, there was, at the 

 end of the Mesozoic Era, a vast ocean containing many 

 islands. In the south lay a great continent, united in the 

 east with Africa and in the south with Australia and New 

 Zealand by way of an antarctic land bridge. Gradually, in 

 early Tertiary times, the northern islands became fused and 

 joined to the southern land -mass, while Australia was dis- 

 connected. During all this time North and South America 

 remained entirely separated. Mammals, however, were able 

 to pass from the latter continent through Africa into Europe, 

 and across a land bridge in northern latitudes to North 

 America. The sea, which had covered the Andean region in 

 Mesozoic times, disappeared early in the Tertiary Era, but 

 certain bays of the Pacific Ocean still remained and ex- 

 tended eastward to the far side of the Andes. During the 

 Eocene Period the Atlantic Ocean advanced from the south, 

 covering part of Argentina and practically separating 

 Brazil from the rest of the continent, while the former land 

 connection with Africa ceased to exist. Towards the end of 

 the Oligocene Period the " Archhelenis " land bridge once 

 more rose to the surface for a brief period and then finally 

 subsided entirely, save for a few scattered islands. 



It would have been particularly valuable to obtain Pro- 

 fessor Osborn's opinions on the geological evolution of South 

 America. We possess only his palaeogeographical maps 



* Ameghino, Fl., " Geologia de la Republica Argentina," pp. 916. 



