18 SOPER— GEOLOGY OF PARAHYBA 



becomes a series of isolated patches overlying the granites and 

 gneiss. 



14. The sedimentary rocks have three main divisions : — a deposit 

 of sandstone, one of limestone, and a more recent deposit of sands 

 and clays. 



15. The sandstone directly overlies the uneven face of the crystal- 

 line rocks. It is of a medium grain, is conglomeritic in places, and is 

 usually of a white or reddish color. It has a thickness of at least 

 30 meters and probably more. It is exposed in a continuous strip 

 from near Aracaty to Natal and probably further south ; its average 

 exposed width is from 8 to 12 kilometers. 



16. In general this sandstone dips gently to the northeast. No 

 fossils are known to have 'been found in it, but on account of its 

 association with the limestone, it is commonly referred to late Cre- 

 taceous or early Tertiary age. 



17. The sandstone is overlain by a bed of hard, fine-grained, 

 yellowish and grayish limestone. 



18. The limestone is exposed in a continuous strip from near 

 Aracaty to Natal and is known to exist in several places between 

 Natal and Parahyba. Its width varies from about 70 kilometers in 

 the vicinity of Mossoro, to 25 kilometers at x\ssu, and less than 10 

 kilometers at Natal. It has a thickness of from 30 to 50 meters. 



19. In general the limestone dips gently toward the sea — to the 

 northeast. It is of late Cretaceous or early Tertiary age. 



20. The contact between the limestone and the underlying sand- 

 stone, is marked from Uniao to Assu, by a low escarpment which 

 varies in height from 30 to 100 meters. 



21. The limestone in turn is overlain 'by a partially consolidated 

 deposit of sands and clays. Where these beds are exposed along the 

 coast they are highly colored and contain much iron. 



22. The area of sands and clays is exposed in a continuous strip 

 from north of Aracaty, to south of Recife. They have a width 

 which varies from 35 kilometers at Mossoro, to about 15 kilometers 

 at Parahyba. Their thickness at Areia Branca is more than 90 

 meters, at IMacau it is 106 meters, and at Natal it is more than 108 

 meters. 



23. At only one or two places along the shore are these sedi- 



