360 
ORIGIN OF LIFE IN AMERICA 
to parts of pre-existing western lands. All through Tertiary 
time the mountains must have continued to rise, though our 
knowledge of later geological history is still meagre. We know 
that Tertiary marine deposits occur in the Orinoco valley, and 
it is likely that a narrow marine channel still separated north¬ 
western South America from the rest of the continent during 
the earlier part of the Tertiary Era. The Amazon valley no 
doubt was at that time a hay of the Pacific ; still, I am unaware 
of any geological or zoogeographical evidence for Professor 
Osborn’s supposition that north and middle South America 
were completely divided in Miocene times by a wide sea. That 
the Orinoco and Amazon valleys were in communication with 
one another for a long time is shown by the fact that one of 
the species of manatees (Trichechus inunguis) and the fresh¬ 
water turtle Podocnemis expansa are confined to the upper 
portions of these two great rivers. A most surprising 
confirmation of the theory that an ocean bay extended to the 
neighbourhood of the Andes has been discovered near the small 
town of Pebas, on the upper Maranon, more than twenty 
degrees of longitude west of the mouth of the Amazon. Pro¬ 
fessor Boettger described deposits from this locality contain¬ 
ing typically brackish water mollusks which could only have 
lived in the neighbourhood of the sea. He naturally came to 
the conclusion that the Atlantic then had invaded the Amazon 
valley so as to extend near to the foot of the Andes. But 
Dr. Katzer’s view, already alluded to, according to which the 
Amazon drainage only changed eastward in later Tertiary 
times, appears to me to agree better with the zoogeographical 
features of eastern South America. Professor Boettger * 
looked upon the Pebas beds as being of Oligocene, possibly 
Eocene age. The fresh-water fish fauna of the Pacific slopes 
of southern Ecuador still exhibits such affinity to that of the 
Amazon that the Ecuador mountains could only have had a 
slight elevation until comparatively recent geological times. 
Hence we may assume that the Pacific extended to the neigh¬ 
bourhood of Pebas when these brackish water beds were laid 
down. 
An interesting zoogeographical demonstration of the 
* Boettger, O., “ Die Tertiarfauna von Tebas,” p. o03. 
