370 PATAGONIAN EXPEDITIONS : ZOOLOGY. 



In the earliest Tertiary tropical America consisted of two land areas, 

 Archiguiana and Archamazona, separated by the lower valley of the 

 Amazon which was still submerged. 



There was a land mass between Africa and South America — possibly 

 in contact with Guiana in South America and some point in tropical 

 Africa. This land mass was inhabited, among others, by Lepido- 

 sirenidcE, Pcecih'idcs, Characida, Cichlidce and Silurida. This land mass 

 sank beneath the surface of the ocean, forcing the fauna in two directions, 

 towards Africa and towards South America, exterminating all types not 

 moved to the east or the west. F"rom these two rudiments have developed 

 the present diverse faunas of Africa and South America, each reenforced 

 by intrusives from the ocean and by autochthonous development, by immi- 

 grants from Africa, also neighboring land areas. The one fauna cannot 

 be said to have been derived directly from the other. 



The connection between Africa and South America existed before the 

 origin of present genera and even before the origin of some of the present 

 subfamilies and families, some time before the earlier Tertiary. There 

 has never been any exchange between Africa and South America since 

 that time. There must have been an intimate connection between these 

 two continents, for there is no evidence, such as identical species or genera 

 on the two coasts, to indicate an occasional or accidental exchange of 

 types across the Atlantic since the formation of existing genera, there- 

 fore, such an interchange across the ocean probably never took place. 

 The East Brazilian land mass south of the Amazon (Archamazona) must 

 have become stocked from the western end of Helenis (Archiguiana) 

 very early, for it contains many genera peculiar to the region, indicating 

 a long separation, and Tertiary fresh-water deposits in this area contain 

 existing genera of fresh-water fishes. The Pacific slope fauna is a more 

 recent acquisition from the east. 



When, later, the Cordilleras arose out of the ocean at a distance from 

 Archiguiana and Archamazona too great to be traversed by colonists from 

 them, their developing streams and arms of the sea, connected with 

 brackish, and later fresh-water lakes, all became populated with marine 

 types from the surrounding sea. In the north where they came in com- 

 petition with immigrants from Archiguiana, most of them were exter- 

 minated with the continued elevation of the land. On the south which 

 was not or was not so early reached by immigrants, Orestias, Gastropterus, 



