I9I3-] 



REGION ABOUT NATAL, BRAZIL. 



441 



The relation of the sand-dunes to the sandstone is clearly de- 

 fined along the sea-cliffs. The older reolian deposits of sand lie 

 cross-bedded on top of the horizontally bedded sandstone and clay 

 series. Above these are blown newly formed sand-dunes. 



Fig. 8. Diagram of the bluffs at Ponte Negra, Rio Grande do Norte, showing 

 the old asolian stratification with the newly formed sand-dunes lying on top. 



The alluvial deposits are extensive, filling the wide river channels. 



Description of the Formations. 



The formations are described in this paper in the following 

 order : 



1. The crystalline rocks, probably Archean, 



2. The limestones, of late Cretaceous or early Tertiary age. 



3. The iron-sandstones and clays, which are later than the 

 limestones. 



4. The alluvial deposits. 



5. The sand-dunes. • 



The Crystalline Rocks. 



The railroad extends twenty-eight kilometers west of Taipu to 

 Baixa Verde. The rocks of this region are crystalline, and a study 

 was made of them here. Beyond Baixa Verde one or two kilo- 

 meters, new railway cuts expose fresh specimens of these rocks, 

 showing something of their general relation to each other. This 

 part of the paper has been taken freely from the notes of Dr. J. C. 

 Branner and Mr. E. Leib. Slides, made from the rocks collected, 

 have been studied and the following report is submitted. 



