42 bulletin: museum of comparative zoology. 



and may be fairly presumed to be of Pre-Cambrian age. In the 

 coastal border gneissoid granites with well-developed augen-structure 

 abound. This rock is nowhere better shown than about Rio de 

 Janeiro, as in the Pao de Assucar at the entrance to the harbor. 

 Apparently of later date than the granite-gneisses are intrusions of 

 phonolite and tinguaite which occur in the form of stocks, while more 

 basic dikes are not wanting. 



In eastern Sao Paulo there is an evidently infolded belt of slates and 

 limestone, seemingly the newest member of the metamorphosed 

 series. The distribution of this formation has not been shown on 

 geological maps. In southeastern Santa Catharina the belt between 

 the Permian border and the coast appears to be entirely granitic, 

 though north of this district quartz-schists are involved in the complex 

 as in the vicinity of Itajahy. 



North and south of the Permian-Triassic basin of south Brazil 

 these Pre-Devonian rocks have a vast extension, stretching far into 

 the interior in the state of Minas Geraes and forming the greater part 

 of Uruguay. In the region south of Rio de Janeiro it is evident from 

 the relations of this series to the overlying Devonian beds that one 

 or more periods of deposition, mountaining-building, and igneous 

 intrusion preceded the deep erosion of the deformed mass as the 

 prelude to the incursion of the Devonian sea. The once eastward 

 extension of this deformed and eroded Pre-Devonian terrane into 

 what is now the basin of the Atlantic Ocean has no assignable limits. 

 The basal beds of the Devonian rest on a westward dipping now 

 slightly warped surface of these older rocks in a manner to show that 

 the sea crept in over a region of little or no relief but how far this 

 peneplaned surface extended to the eastward there are no definite 

 facts to show. 



The Devonian Terrane. — The Devonian of south Brazil occupies 

 a narrow belt of outcrop along the eastern margin of the Permian area, 

 disappearing on the north in Sao Paulo and on the south in Parana. 

 As strata of Devonian age reappear far to the northwest at Cuyuba 

 in Matto Grosso, the Devonian is thought to extend beneath the 

 Permian and Trias over a vast area. It is agreed that the Devonian 

 of South Brazil includes at its base -the thick, light-colored sandstones 

 which form the Serrinha and the Serra das Furnas. This formation 

 is overlain by fossiliferous shales of Mid-Devonian age. The De- 

 vonian shales are intruded by numerous dikes and sills of diabase 

 whose outcrops maj^ be seen in the vicinity of Ponta Grossa. Their 

 date of intrusion is probably Triassic. The absence of the Devonian 



