woodworth: geological expeditiox to brazil and chile. 41 



IV. OUTLINE OF THE GEOLOGY OF SOUTH BRAZIL. 



For the understanding of the relations of the Permian glacial 

 deposits of south Brazil it is proper to give a resume of the geological 

 structure of the country. Passing over the pioneer work of Lieut. 

 Colonel Wilhelm L. von Eschwege, whose Mritings are lithological 

 rather than geological, the main outlines of this structure are to be 

 found in the publications of Dr. Orville A. Derby and his associates, 

 Dr. J. C. Branner's resume in his Geologia element ar, and in Dr. I. C. 

 White's Report on the coal area. In this resume the observations of 

 the writer have been allowed to a limited extent to enter into the 

 interpretation of certain features of the region. 



The formations which enter into the structure of this part of Brazil 

 may be grouped in the following terranes: — L The Pre-Devonian 

 or igneous and metamorphic belt of the coast including the Serra do 

 Mar region, frequently classed as Archean. 2. The Devonian 

 including the sandstone cuesta of the Serra das Furnas and the over- 

 lying fossiliferous shales of Ponta Grossa in the state of Parana. 3. 

 The Permian beds, including conglomerates, tillite beds, as well as 

 sandstones and shales, the latter coal-bearing in the south. 4. The 

 Triassic sandstones and trap sheets; the latter making the escarpment 

 known as the Serra Geral and its topographical equivalents elsewhere. 

 5. The Tertiary fresh-water deposits of the upland and possil)ly along 

 the coast. 6. The Recent deposits along the coastal border now 

 slightly elevated. 



The Pre-Dcvonian Terrane. — The Pre-Devonian belt is here so- 

 called because it comprises a complex of igneous and metamorphosed 

 sedimentary rocks unconformably overlain by the westward dipping 

 Devonian sandstones and shales of the upland, as yet the oldest known 

 fossiliferous group in the region. The use of the term Archean or 

 Pre-Cambrian for this complex seems at present inadvisable because 

 of the possibility that certain of the metamorphosed clastic members 

 of the series may be of Lower Silurian (Ordovician) or Cambrian age 

 analogous in their structural relations to those of these ages in the 

 metamorphic belt of the Piedmont terrane of the Atlantic slope of 

 North America. 



In the latitude of Rio de Janeiro this belt of complex rocks includes 

 the elevations known as the Serra do Mar and an inner line of moun- 

 tainous relief known as the Serra da Mantiqueira. Gneiss of unde- 

 termined origin appears to be the most ancient member of the region 



