DEVELOPMENT OF SOUTH AMERICA 
343 
ocean strait extended from the north side of Guiana across 
Venezuela and Colombia to Peru during the Cretaceous 
Period. During all this time, and even in early Tertiary 
times, the waters from the old eastern land continued to 
drain westward towards the Pacific. The persistent rise of 
the newly formed Andean mountain chain resulted at first 
in the formation of a vast lake covering the entire Jowlands 
of the Amazon valley area. Eventually, in Miocene times, 
according to Dr. Katzer,* the drainage was reversed, with the 
result that the Amazon river flowed for the first time into the 
Atlantic Ocean. Concurrently North and South America be¬ 
came united through the Central American land bridge. 
Professor Ivoken’s f palaeogeographical maps were con¬ 
structed as the outcome of a combination of geological and 
palaeontological studies. South America, he remarks, had 
already assumed its present shape and form in Cretaceous 
times, though it did not extend so far west as at present except 
in Ecuador and Colombia. It was separated from all other 
continents but Africa. In early Tertiary times South America 
became entirely isolated. Argentina and southern Chile were 
largely flooded by the sea, while a long gulf filled the whole 
valley of the Amazon as far east as the Andes. 
Dr. Arldt,J who included the distribution of living animals 
and plants as well as palaeontology within the sphere of his 
studies, gives a series of highly complex maps which cannot 
readily be described. His conception is that South America 
in Lower Cretaceous times was somewhat like that described 
by Professor Koken, viz., an extension of land eastward as far 
as Africa and a simultaneous submergence of the west coast. 
Towards the end of the Mesozoic Era, that is to say at the end 
of the Cretaceous Period, a complete change in the conditions 
of land and water supervened. South America was then 
divided into two parts by an interoceanic connection across 
the Amazon valley. The northern portion, consisting of 
Colombia, Ecuador and Guiana, is supposed to have extended 
westward across the Galapagos islands as far as the Sandwich 
* Katzer, F., “ Geologie des Amazonengebietes,” pp. 239—262. 
f Koken, E., “ Die Vorwelt,” Maps 1 and 2. 
X Arldt, J., “ Entwicklung der Kontinente,” Maps 19 and 20. 
