38 W'ind/uttist'ii — The Cretaceous- Tertiary 



Pampa this range is known from the Rio Colorada as 

 far as the southern limit of the Province of Cordoba. 89 

 It is apparently cut off by transverse faults at the south 

 of the Rio Colorada, between the 66th and 64th degrees 

 west of Greenwich. There is no doubt that the southern 

 border was more elevated in the past and influenced the 

 extension of the San Jorge-Sea. 



Towards the east, the Sierras of the Province of 

 Buenos Aires represent the remains of a region which 

 has to be regarded as part of a continental mass during 

 this same period. 90 The studies of Keidel revealed a 

 part of the structure of this region and opened the way 

 to future investigations. Its internal structure was 

 determined by Permian movements, the regional char- 

 acter of which Keidel emphasized. These movements 

 here created a zone which for a considerable length of 

 time was one of the most prominent centers of regional 

 erosion. Doubtless its area was considerably larger 

 than the present one, which physiographically is repre- 

 sented only by the two ranges shrunk up and folded by 

 Tertiary movements. Certain connections of this region 

 are known, westward with the Precordillera of San Juan 

 and Mendoza, and eastward with the mountains of South 

 Africa. It has, however, been pointed out in Part I, that 

 the floor (" socle") of these ranges formed a firm barrier 

 to the older Patagonian transgressions. It did not sub- 

 merge before the close of the Miocene, probably at the 

 time of uplifting and folding of these ranges, and the 

 formation of the Middle Atlantic basin was a consequence 

 of the breaking down of this barrier. For the scope of 

 this paper it is sufficient to repeat these facts and to 

 maintain the assertion that no trace of the San Jorge 

 can be found in the regions northward from here. 91 

 Further, it is remarkable that traces of Roca-deposits 



88 See Stappenbeck, Investigaeiones hidrogeologieas de los valles de 

 Chapalco y Quehue y sus alrededores, Boletin 4B, Direccion Gral. de Minas 

 etc., Buenos Aires, 1913. 



80 Compare what has been said about the theory of ' ' Archhelenis ' ' in 

 Part I. 



81 The presence of Ostrea guaranitica in Misiones reported by Ameghino 

 (Les formations sedimentaires, p. 43) is doubtful. In the same mariner 

 must we regard the assertion of v. Ihering (Katalog der Mollusken etc., 

 pp. 21, 22) that fragments of Ostrea guaranitica and Ostrea neuquena were 

 found at Arroyo San Juan, Puerto de Santa Ana, Misiones. There are 

 really no deposits with oysters in this region, and the specimens in question 

 are not correlated either with the so-called ' ' Formaeion Guaranitica ' ' or 

 with the origin assigned to them. 



