840 ORIGIN OF LIFE IN AMEEICA 



the south it was still joined to the Antarctic Continent, which 

 had then become separated from Australia. In the north, it 

 had lost its land connection with. North America, which it did 

 not regain until later Tertiary times. 



To a certain extent the views of the two authors agree, at 

 any rate, in the assumption that the continent of South 

 America is composed of several originally independent land- 

 masses, one of which was joined to Africa. The most striking 

 difference in their opinions, apart from the geological period 

 during which the various elements are supposed to have be- 

 come fused together, lies in Dr. Ortmann's conception of 

 three totally distinct land-masses, while Dr. von Ihering only 

 recognises two. Nevertheless, even the latter acknowledges 

 the faunistic division of his " Arohiplata " into a northern 

 and southern portion, although his nomenclature is apt to be 

 somewhat confusing. Dr. von Ihering informs us (p. 177) 

 that the old Archiplata fauna has no close relationship to 

 that of the rest of South America. 



A third contribution to the geological history of South 

 America is furnished by another group of fresh-water animals, 

 namely, the fishes. The tropical American fresh-water fauna, 

 having its centre of greatest diversity in the middle Amazon 

 basin, says Professor Eigenmann,* is attenuated northward 

 till it reaches the vanishing point just on the borders of 

 the United States. Southward it extends to somewhere south 

 of Buenos Aires. The Patagonian and North American 

 faunas are entirely different from the tropical American fauna 

 and from each other. The results of his studies are that the 

 existing distribution of the fresh-water fishes can only have 

 been brought about by the supposition that tropical America 

 in early Tertiary times consisted of two land areas (" Archi- 

 guiana " and " Archamazona "), separated by the lower valley 

 of the Amazon, which was submerged by the sea. There was 

 a land-mass between Africa and South America, possibly 

 joining Guiana and tropical Africa. But this connection, he 

 urges, must have ceased to exist before the origin of the 

 present genera, and even before that of some of the families. 



* Eigenmann, C. H., " Freshwater Fishes of South America," pp.;517 

 —528. 



