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 lowlands 

 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 Koken'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 de3 Amazonengebietes," pp. 239—262. 



t Koken, E., " Die Vorwelt," Maps 1 and 2. 



X Arldt, J., " Entwicklung der Kontinente," Maps 19 and 20. 



