96 J. C. BRANNER — GEOLOGY OP NORTHEAST COAST OF BRAZIL 



Analysis of Limestone from near Penha 



L. D. Mills, analyst. 



I. II. 



Lime (CaO), 29.08 29.05 per cent. 



Magnesia (MgO) 20.10 19.92 per cent. 



Inasmuch as limestones and dolomites are common in the Cretaceous 

 beds farther south, and as no limestones have been found in the beds of 

 known Tertiary age, it seems probable that these limestones may be 

 Cretaceous. 



Looking south from Curimatau station, the Tertiary (?) hills have the 

 appearance of a flat-topped plateau. At Curimatau station the railway 

 first comes upon the gneiss, which is here exposed by stream erosion in 

 this deep, broad valley. These rocks in place are visible at the railway 

 station and also at the bridge over the river. 



After leaving Rio Curimatau the soil is pebbly for several kilometers ; 

 beyond this it is sandy. Then follow the Tertiary beds, and these are 

 succeeded by crystalline rocks. 



These crystalline rocks begin on the plateau about 5 kilometers be- 

 yond Rio Curimatau. 



At Montanha station the rocks are granites and the land is gently 

 rolling. Some quartzitic or cherty rocks seen at Natal on the cars are 

 said to have come from kilometer 108, north of Montanha station. 

 These rocks appear to be Paleozoic, but without farther examination or 

 evidence nothing trustworthy can be said of their age. 



About 1 kilometer north of Montanha, Tertiary (?) beds are visible. 

 These are followed by granites, which are exposed here and there as 

 exfoliated boulders and bosses. Farther on the Tertiary appears in 

 patches again, and these in turn are followed by granites and gneisses, 

 which continue to Nova Cruz (kilometer 121). 



In the low grounds along watercourses and on some of the slopes the 

 vegetation is thick and rank, but across the high flat Tertiary plateaus 

 it is sparse, and in many places so much so that the ground is bare and 

 hard and the landscape desert-like. 



CONCLUSIONS REGARDING THE GEOLOGY OF RIO GRANDE DO NORTE 



The facts of geologic interest in the section along the Natal a Nova 

 Cruz railway are as follows : 



1. The horizontal weathered Tertiary (?) beds common along the coast 

 southward nearly to Rio de Janeiro form a belt from 15 to 25 kilometers 

 wide through the region traversed by the Natal a Nova Cruz railway. 



