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 o»f 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 somewdiat 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, II. F., “Age of Mammals” Maps, pp. 64, 137, 183 and 245. 
t Lapparent, A. de, “ Traite de Geologie,” 4th ed., pp. 1376 and 1455. 
