344 OKIGIN OF LIFE IN AMERICA 



islands, thus forming a great peninsula of land which like- 

 wise was joined to lower California and western Mexico. The 

 southern part of South America was then still united by a 

 narrow land bridge with Africa, while the western side of it 

 now became joined to a great belt of land extending right 

 across the Pacific Ocean to New Zealand and Australia. In 

 early Tertiary times South America became separated from 

 North America and the Sandwich islands, while the two 

 sections of the continent fused in the west. The African 

 and Australian land connections still persisted in a modified 

 form. 



We can gather from all these expressions of opinion as to 

 the past geological history of South America that there is 

 comparatively little general agreement on the subject. Some 

 points, however, seem to be fairly well established. All 

 authorities concur in the belief that the Eastern highlands of 

 Guiana and Brazil have been land surfaces since the begin- 

 ning of the Secondary Era, at any rate, and on these, there- 

 fore, we ought to find relicts of a Mesozoic fauna. All the 

 writers quoted also agree that at some time or other during 

 the Tertiary Era there was either a complete interoceanic 

 connection along the Amazon valley or a long gulf of the ocean 

 extending for some distance inland. Yet there is an im- 

 portant difference of opinion as to whether this gulf belonged 

 to the Atlantic or the Pacific Ocean. But since most of the 

 writers contend that the central portion, at any rate, of the 

 Andes is made up largely of Jurassic and Cretaceous marine 

 deposits, while the eastern parts of South America were land 

 in Mesozoic times, it seems more reasonable to assume, with 

 Dr. Katzer, that the Pacific Ocean extended eastward as far 

 as the archaean highlands of Brazil and eventually retreated 

 so as to leave only a Pacific gulf on the site of the existing 

 upper Amazon valley. In view, however, of the fact that the 

 Pacific Ocean must have been completely shut out from South 

 America by the western belt of land above alluded to, it was 

 really the waters of the Atlantic Ocean which flooded western 

 South America as far east as the highlands of Brazil (com- 

 pare Fig. 14). 



Several of the authors cited recognise a faunistic relation- 

 ship between Australia as well as between Africa and South 



