112 NEW YORK STATE MUSEUM 



southeast. The southernmost of these, the Sierra de la Ventana, 

 is according to Suess (v. 3, pt 2, p. 546) a branch of the Andes; 

 the Sierra Tandil, however, is regarded by him as a border formation 

 of the Brazilian mass, the latter itself having been reached in a 

 boring at Buenos Aires at a depth of 300 meters. 



While there is thus no doubt of the existence of a great Precambrian 

 basement complex, the " Brazilian mass," in South America, the 

 folds and strikes of this complex seem everywhere so involved 

 with later orogenic movements that no safe conclusion can be 

 reached regarding the Precambrian fold directions. We believe, 

 however, that some of this folding bears the earmarks of posthumous 

 orogenic movements and may thus indirectly give a suggestion of 

 probable Precambrian trends 1 (see next chapter). 



Evidence from Posthumous Folding 



Richthofen not only recognized the remarkable persistency of 

 the northeast-southwest folding in the Precambrian basement 

 complex of northeastern China, but also observed that the later 

 mountain ranges are inclined to fall in with the same direction. 

 R. Godwin Austen (1856, p. 62), however, in his famous treatise, 

 " On the Possible Extension of the Coal-measures beneath the South- 

 eastern Part of England ", had recognized already long before that 

 younger folds of Mesozoic age extend from Belgium into southern 

 England and follow the trend of the ancient Paleozoic folds; and 

 he had " even maintained " (see Suess-Sollas, v. 11, p. 93) "as a 



1 E. Jaworski (Das Alter des sudatlantischen Beckens. Geol. Rundschau, 

 12:68, 1921). states that the north-south trend of the Precambrian beds, south 

 of Cape St Roque (the farthest eastern region of Brazil) is established. 



The same author points to the occurrence of a gneiss block on Tristan d'Acunha, 

 to the granite foundation of Ascension island, the peridotite composition of St 

 Paul and the finding of coarse sands of plutonic rocks and crystalline schists 

 at the bottom of the south Atlantic (by Phillipi, see Andr6e, Geologie des Meeres- 

 bodens, v. 2, 1920) as connecting elements between the Precambrian massifs 

 of Africa and Brazil and as indicating the late existence of a South-Atlantic 

 land of Precambrian rocks. 



H. Keidel (op. cit., 19 13 and 191 6) has found that the Precambrian folding 

 (extending to Permian time) and strike is dominantly northwest, in contrast 

 to the north-south strike of the Tertiary Andine folds, in western Argentina 

 and the Pampine sierras, with a subordinate northeast-southwest strike of Pre- 

 cambrian faulting. G. Bodenbender (El nevado de Famatina, Bol. Acad. Nac. 

 Cient. Cordoba, 1916, p. 100-82; review by H. Gerth in N. Jahrb, 209-11, 1921) 

 records north-south folding in the Precambrian of the Pampine sierras. The 

 prevailing northwest strike of the Precambrian can be traced to the Upper 

 Marafion, as we saw before. The Precambrian of Argentina and western Brazil 

 may then exhibit either marginal phenomena of the Archean Gondwana structure, 

 with an average north-south direction, or have been part of another continental 

 mass, extending westward. The former conclusion seems to be supported by 

 Keidel's last important publication on the precordillera of San Juan and 

 Mendoza in western Argentina (ibid., 192 1, p. 97) in which he considers this 

 range and its component Ordovician, Silurian, Devonian and Gondwana glacial 

 beds as indicating the western border of a part of the Gondwana continent. 



