1902.] AND ANCIENT GEO GRAPH V. 361 



Cordilleras in Peru and Bolivia many exposures of old (*Archaicand 

 Paleozoic) rocks; but the fact that in this region (from Colombia 

 to Bolivia) Lower Cretaceous of the Mediterranean type has been 

 discovered right in the Cordilleras, 1 renders it possible that those 

 older rocks were originally covered by Mesozoic deposits, which 

 were removed subsequently by erosion ; and this is also the view of 

 Suess (1885, p. 684, and 1888, p. 683), since he takes it for 

 granted that the Cretaceous beds of the Upper Amazonas (and 

 Orinoco) valley once continued across the whole continent to the 

 Pacific Ocean. 



Thus there would result, in Lower Cretaceous times, a complete 

 separation of Central from South America by a sea, which extended 

 from the region of the mouth of the Orinoco westward to Ecuador 

 and Peru, connecting the Atlantic and Pacific Oceans : in the Upper 

 Cretaceous, however, Guiana was united with Ve?iezuela. 



The Potamocarcinince, which, as we have seen above (p. 35 1), 

 arrived in Guiana in the Upper Cretaceous (by way of the connec- 

 tion with Africa), found at this same time a land connection with 

 the northern parts of Venezuela, and generally with the Antillean 

 continent, and this explains their general distribution over Central 

 America and the West Indian region, as set forth above (p. 308), 

 and the origin of this distribution consequently falls in the Upper 

 Cretaceous. 



d. South America. 



The separation and isolation of South America from Central, 

 lesp. North America during Mesozoic times as well as in the begin- 

 ning of the Tertiary, forms the fundamental idea of von Ihering's 

 Archiplata and Archhelenis theory (1891). But, according to him, 

 the line of separation was situated in the present Amazonas valley, 

 and existed during the Jurassic, Cretaceous and the Eocene; in the 

 Oligocene the elevation of the Cordilleras began, and Archiplata 

 (the southern part) was united with Archiguiana (Guiana and 

 Venezuela), and it was not until the beginning of the seond half of 

 the Tertiary (Miocene) that these latter parts became united with 

 North America by the formation of the Isthmus of Panama. 



We can accept this view only in part, since the very important 



1 Hyatt, A., in Proc. Boston Soc. Nat. &ist.,Vo\. 17, 1875, p. 3 6 5 &'» Stei " 

 mann, in N Jahrb. Mineral., etc., 1 88 1, 2 p. 1 30 ff., 1882, 1 p. 166 ff. f and 

 Gerhardt, ibid., Beil., Bd. 11, 1897. 



