342 ORIGIN OF LIFE -IN AMERICA 



founded upon the distribution of fossil mammals. It is sur- 

 prising that in these maps South America in late Cretaceous 

 and basal Eocene times, is represented as almost precisely 

 what it is to-day, except that it is continued southward across 

 an antarctic continent to Australia. In the middle Eocene, 

 South America differs only in so far as a long bay of the 

 Atlantic has entered the Amazon valley. There are no indica- 

 tions of any land bridges at that time, South America being 

 completely isolated from all other continents. During the 

 Oligocene Period it still remained so, but the sea made 

 further inroads on the Amazon valley, it encroached on the 

 valley of the Parana river and flooded a large part of Argen- 

 tina, reducing southern Chile to a few islands. It is only in 

 Miocene times, according to Professor Osborn,* that South 

 America became divided into two parts by a broad gulf ex- 

 tending from the Atlantic to the Pacific across the Amazon 

 valley. 



Geologists, except Dr. Katzer and Professor de Lapparent,f 

 have as a rule dealt with the problem in a less comprehensive 

 manner. The ideas of the latter differ from the authors cited 

 in so far as the main permanent land-mass at the end of the 

 Mesozoic Era in South America was confined, in their opinion, 

 to the east. They suppose the highlands of Guiana, eastern 

 and southern Brazil to have been united. All the rest of the 

 continent was then under water. At the commencement of 

 the Eocene Period, according to Professor de Lapparent, 

 Central America had come into existence, but disappeared 

 again shortly after, while a broad marine channel stretched 

 from the Pacific to the Atlantic between northern Chile and 

 Argentina. Dr. Katzer's views are somewhat similar. He 

 dees not believe in the Atlantic Ocean having invaded South 

 America from the east. In the beginning of the Mesozoic Era 

 the area of archaean rocks and later palaeozoic deposits of 

 Guiana and Brazil formed a large connected land-mass. In 

 Upper Jurassic times, he says, the old land connection be- 

 tween South America and South Africa on the one hand, and 

 between South America and Australia, still existed. An old 



* Osborn, H.T., "Age of Mammals" Maps, pp. 64, 137, 183 and 24e. 

 t Lapparent, A. de, "Traite de Geologie," 4th ed., pp. 1376 and 1455. 



