-26 Studies in Geology, No. 3 



caused the diversion of the southern current might well 

 have allowed the Chilean forms access to the north Peruvian 

 waters during Variegated time. 



Ortmann/^ in discussing the possibility of a separation 

 of South America into two masses according, to the "Arch- 

 hellenis — Archiplata" theory of von Ihering, points out 

 the dissimilarity of the north Peruvian faunas from those of 

 Navidad, Chile, and Patagonia in support of the hypo- 

 thetical central seaway as a barrier to the intermingling of 

 the regional faunas. It does not seem necessary to pre- 

 suppose so vast a change as the splitting apart of South 

 America in order to explain the difference between faunules 

 which by virtue of their location alone might be expected to 

 differ. All data so far collected indicate that there is un- 

 broken structural and geologic continuity along the Andean 

 axis from Panama to the Straits of Magellan. The exis- 

 tence of norrh-south lines of tectonic weakness is established 

 both through the immense Andean uplift and the sunken 

 blocks which hayjfe given rise to the famous deeps off the 

 west coast, and it is extremely unlikely that a major line of 

 weakness existed in comparatively recent times at right 

 angles to these known. The sea separating "Archhellenis" 

 and "Archiplata" would have had to be deep enough to 

 prevent the migration of molluscs, and broad enough to 

 forbid the passage of free-swimming larvae. Evidence of 

 so great a break in the continental mass of western South 

 America, which should be discernible if the seaway existed, 

 apparently is not present, the general geologic situation on 

 the west coast suggesting complete continuity, with no hint 

 of a break. ^® There may have been, and probably was a 

 profound embayment of the Amazon basin, but submergence 

 of the site of the Andes is not evident from observations thus 



" Princet. Exp. Patag., vol. 4, p. 298, 1901 ; also pp. 319-324. 

 "See Berry, E. W., Geol. Soc. Am. Bull, vol. 29, pp. 637-648, 

 1919; Proc. Pan Pacific Sci. Conf. pp. 845-865, 1921. 



