PROCEEDINGS 



OF THE 



AMERICAN PHILOSOPHICAL SOCIETY 



HELD AT PHILADELPHIA 

 FOR PROMOTING USEFUL KNOWLEDGE 



Vol. LII September-October, 1913 No. 211 



GEOLOGY OF THE REGION ABOUT NATAL, 

 RIO GRANDE DO NORTE, BRAZIL. 



(Plates XV.-XXIL) 



By OLAF PITT JENKINS. 



{Received May sg, 191 3.) 



Introduction. 



The state of Rio Grande do Norte is one of the smallest in Brazil ; 

 it has an area of 57,485 square kilometers, and lies wholly within 

 the tropics. The climate, topography and geology of this state 

 may be taken as a type of the geology of the northeastern coast of 

 Brazil. 



Topographically the region is one of rather low relief, the climate 

 is semi-arid, and in places the soil is thin. The general geology is 

 simple, consisting of an old series of crystalline rocks, probably of 

 Archean age, over and upon which rests a coastal belt of Cretaceous 

 or Tertiary sediments having a width of about thirty kilometers. 

 There are some mountains of fair size in the interior, but they are 

 nearly all of granites or other crystalline rocks. None of these 

 mountains lie within the area discussed in the present paper. 



In 1909 I published in the BuUetin of the Geological Society 

 of America a paper on the geology of the Northeastern Coast of 



PROC. AMER. PHIL. SOC, LII. 211 J, PRINTED SEPT. l6, I913. 



