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, FI., “ Geologia de la Republica Argentina,” pp. 9—16. 
