102 bulletin: museum of compatative zoology. 



placed upon the epoch of dissection. (Branner, 1906, p. 283. A. S. 

 Woodward, 1898, p. 63-75). Some warping of the surface has appar- 

 ently taken place since the Tertiary beds were deposited. 



At the northern limits of the region under discussion the Serra da 

 iVIantiqueira rises as a long lofty monadnock range in the Pre-Devonian 

 terrane. The western slope of the crest of this gneissic mass subtends 

 the surface of contact of the Permian of Sao Paulo upon the same 

 ancient rocks. It therefore appears probable that in the Serra da 

 Mantiqueira we have a remnant of the Permian floor east of the 

 present line of outcrop of those strata. 



Between the Serra do Mar and the escarpment formed by the 

 westward dipping Devonian sandstone cuesta ^ there is a high level 

 tract belonging to the planalto or tableland. On the South in the 

 headwater region of the Iguassu about Curytiba it is essentially a 

 peneplain and swamps of great extent exist locally. But in south- 

 eastern Sao Paulo an Atlantic stream, the Rio Ribeira de Iguape, has 

 breached the Serra do Mar and gnawed a deep ravine with its head- 

 waters pushed against the crystalline Serra da Paranapiacaba for a 

 watershed. The situation of this stream, the single example of any 

 size to push its headwaters past the Serra do Mar and drain the 

 planalto, in the great concave arc formed by the Paranapiacaba and the 

 Devonian sandstone cuesta is evidently an eft'ect of the Devonian 

 sandstone ridge. The almost level crest of this Serra indicates the 

 approximate level of the Cretaceous peneplain up to w^hich level the 

 plateau was filled with rocks before the present valleys and widened 

 out lowlands of the planalto were excavated. Under these conditions 

 the Devonian sandstones must have extended much to the eastward, 

 possibly to the Serra do Mar crest. In the dissection of the country 

 east of the present retreatal escarpment of the Devonian sandstones 

 the Rio Ribeira de Iguape, protected from capture by the westward 

 flowing streams, has worked backward following the shifting of the 

 watershed formed by the retreating cuesta until its headwaters are in 

 a position almost to capture the Rio Yapo and the uppermost Iguassu. 

 (See map, Fig. 7, p. 43.) The short course and steep gradient of the 

 river have enabled it to cut its present profound ravine. A similar 

 history probably is true of the Rio Tuberao which in southeastern 

 Santa Catharina has excavated its valley across the granitic terrane, 



I The term cuesta used in a technical sense in North American writings on geo- 

 morphology for ob\'ious reasons is not adoptable in Portuguese. "Costa do outeiro" 

 misses the point in the EngUsh use of the Spanish name cuesta. Serra monoclina 

 expresses in structural terms the essential characteristic of a cuesta. 



