376 ORVILLE A. DERBY 



almost perfect parallelism with the coast-line and with the river Sao 

 Francisco (above the great bend at Cabrobo), with a general northerly 

 trend from about latitude 20° 30" to about latitude 9°, where the 

 river Sao Francisco, after making a sharp bend to the southeast, 

 cuts through the range or, more probably, flows past its northern 

 end. Throughout this extension of over 1,000 kilometers, this zone 

 forms the eastern rim of the Sao Francisco basin, which receives the 

 drainage of its western portion, while its eastern drainage goes directly 

 to the Atlantic through the rivers Doce, Jequitinhonha, Pardo, Rio 

 de Contas, Paraguassu, Itapicuru, and Vasabarris. In the upper 

 part of the basins of the Rio das Velhas, Jequetinhonha, and Para- 

 guassu, and to a less extent in that of the Rio de Contas also, the 

 drainage courses correspond approximately with the north-south 

 trend of the serra, while, after escaping from it, the Rio das Velhas 

 and the Jequitinhonha flow for a considerable distance in general 

 paralleHsm to its margins. As certain structural features are more 

 apparent in the northern than in the southern section of the range, 

 our examination can best be made from north to south. 



The Sao Francisco, at some 80 kilometers below the great bend 

 at Cabrobo, where it changes from a northeast to a southeast course, 

 enters a zone of sandstone country which lies in the line of prolonga- 

 tion of the Serra do Espinhafo, though it is somewhat doubtful if 

 it should actually be included in that range. This zone extends from 

 near the mouth of the small river Pajahu to near the great cataract 

 of Paulo Affonso, with a width, along an east-west hne, of at least 

 50 kilometers, while away from the river the width appears to be 

 much greater. The river, which above this zone flows over a bed of 

 gneiss and granite, enters the sandstone belt at an elevation of about 

 330"^ and leaves it at an elevation of about 300"^, to again flow over 

 gneiss, granite, and syenite, in which it has excavated a deep canyon 

 that contains one of the most notable of Brazihan cataracts. The 

 sandstone therefore rests on a nearly horizontal base of truncated 

 crystalline rocks (a peneplain ?) with a i^^-ian elevation of about 300™, 

 and rises in table-topped hills and ridgt ^ on each side to about an 

 equal elevation, or approximately 6oo""''^*^^ove the level of the sea. 



The sandstone is moderately hard, usually coarse-grained, with 

 frequent inclosed pebbles, which in some layers become sufficiently 



