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Annals of the Carnegie Museum. 



studies, several geologic problems developed, which it is believed worth 

 while to set forth, together wath such data as were obtained concerning 

 them. The water studies involved journeys in two general areas, the 

 northern one embracing parts of the states of Pernambuco, Parahyba, 

 Rio Grande do Norte, and Ceari; the southern one being in the State 

 of Bahia. The location of the region is shown on the index map, 

 Fig. I. 



Fig. I.- Index Map of South America, showing location of the region 

 under discussion. 



As a whole this region constitutes a plateau, rising gently inland 

 from the coast to mean elevations of 200 to 400 meters. There are 

 no great mountain ranges, but numerous small ranges and isolated 

 hills rise above the mean levels, and several tablelands rise to eleva- 

 tions of 600 to 900 meters above sea-level. The channels of the 

 streams trend fairly directly to the coast, being almost throughout 

 their courses wide and sandy, with low gradients. Most of the streams 

 are dry during a great part of the year, for much of the region receives 

 but uncertain rainfall and suffers from periodic droughts. 



Geologically, the area as a whole has a basement series of gneiss 

 and crystalline schists referred to by Dr. Branner as the Brazilian 

 complex, 1 intruded by granite and by dike rocks and overlain by 



' Geologia Elementar, by John C. Branner, 2d ed., Rio de Janeiro, 1914, p. 289. 



