Boundary in South America. 1 3 



Parana and Paraguay Rivers. Second, Keidel's dis- 

 covery of the connections between the Sierras of Buenos 

 Aires and the South African mountains 34 establishes 

 (apart from a stratigraphic analogy concerning the Pale- 

 ozoic) a connection of the Permian orogenetic movements 

 in both parts of the southern hemisphere. 



These well-founded observations will, I believe, justify 

 an attempt at reconstruction of this barrier, the ' ' Arch- 

 helenis" in the sense of H. v. Ihering. Evidently, the 

 southern limit of this bridge between South America and 

 Africa coincided approximately with the 38th degree 

 S. L. 35 



Furthermore, the geologic age of the Parana Forma- 

 tion affords the evidence for fixing those diastrophic 

 events which caused the breaking down of the Afro- 

 American barrier and, consequently, the formation of the 

 Middle Atlantic basin. 36 This occurred approximately at 

 the time of the Miocene-Pliocene boundary. A general 

 study of the Chilian Tertiary confirms such opinion ; for 

 the emergence of the Mid- American landbridge (Isthmus 

 of Panama) and the definite closing of the old marine 

 animal route from the South American westcoast to 

 Eurasia, were merely connected events, plainly recorded 

 and attested by many facts. 37 This was the period, when 



84 La geologia de las Sierras de la Provincia de Buenos Aires y sus 

 relaeiones con las montanas de Sud Africa y los A n des, Anales Minist. de 

 Agricultura, Secc. Geologia, 11, No. 3, Buenos Aires, 1916. 



35 In a recent paper, W. D. Matthew (Climate and Evolution, Annals 

 New York Academy of Sciences, 24, 1915) opposes assumptions of "bar- 

 riers and bridges," also certain geotectonie hypotheses. It is true that 

 former speculations on migrations of faunae and floras have been very liberal 

 in the construction of such bridges, but those attempts cannot be compared 

 with the present case, in which stratigraphic, geotectonie and paleontologic 

 facts agree perfectly in the assumption of a continental mass lying in the 

 Middle Atlantic regions. Where this sunken continental mass connected 

 with the present South American Continent is clearly indicated by the 

 absence of Early Tertiary sediments over a large tract of the present 

 coast. 



86 These epirogenetic movements seem to have been allied with the oro- 

 genetic movements which led to the formation of the Sierras of Buenos 

 Aires. According to Keidel, these sierras as orographic elements were 

 formed in the Tertiary, perhaps by large overthrusts coming from the south- 

 west; but it has not been hitherto possible to get a closer determination 

 of age. I believe that the history of Tertiary transgressions may be 

 profitably used for this object. This method would indicate an approxi- 

 mately Upper Miocene age of these movements. 



37 The fauna of the Navidad Beds (Upper Oligocene or Miocene) is of 

 an essentially Atlantic character. The vast Oligocene and Miocene strata 

 of the Peruvian coast are in obvious relation to the Atlantic Ocean and 

 especially to the Caribbean province. Later, in the Coquimbo Beds 

 (Pliocene) the faunistie character changed on the entrance of Indopacific 



