AND RIO GRANDE DO NORTE, BRAZIL. 13 



meters. Their thickness increases as the coast is approached. At 

 Areia Branca they have a thickness of at least 90 meters, at Macau 

 of 106 meters, and at Natal of at least 108 meters. I have never 

 found any fossils in them, but Dr. J. C. Branner' describes fossils 

 in yellowish, calcareous sandstone along the coast at Ponta de 

 Pedras, which he refers to the Tertiary. It is very probable, though 

 of course not certain, that these beds are to be correlated with the 

 sands and clays here described in Parahyba and Rio Grande do Norte. 

 The geologic history of this part of the coast of Brazil, basing 

 our opinion upon the information already given, must have been 

 about as follows : the rocks of the basal complex or the crystalline 

 mass after a long period of erosion were finally submerged along 

 the coast of Parahyba and Rio Grande do Norte during Cretaceous 

 or Pre-Cretaceous times. The sea encroached on the land, much 

 further than the present contact between the crystalline and sedi- 

 mentary areas. It was during this first period of subsidence that 

 the coarse-grained sandstone was deposited. Following this deposi- 

 tion a moderately pure limestone was laid down directly on top of 

 the sand. Whether or not the land rose and the sandstone was sub- 

 jected to erosion before the limestone was deposited, is not known 

 definitely. The exposures of bedded sandstone are few, but where- 

 ever noted the strata of sand and limestone were conformable. 

 Therefore, I am of the opinion that both were laid down during the 

 same period of deposition, but that the contact marks a great change 

 in physical conditions. Following this period the land rose. Ap- 

 parently there was little disturbance for the beds are horizontal 

 or they dip gently toward the sea. Considerable erosion must 

 have taken place at this time for the limestone is worn very thin in 

 places. During Post-Cretaceous times the land along the coast was 

 submerged again and the more recent beds of sand and clay were 

 deposited. Physical conditions must have again changed for the 

 absence of calcareous matter in these latter beds show that animal 

 life was scarce. Once more the land rose and has probably remained 

 above the sea from that time until the present day. The surface of 



"^ J. C. Branner, " Geolog>' of the Northeast Coast of Brazil," Bulletin of 

 Geological Society of America, Vol. XIII., p. 47. Rochester, 1902. 



