344 
ORIGIN 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 
