14 SOPER— GEOLOGY OF PARAHYBA 



the sand and clay deposits is more or less calcareous due to the lime- 

 laden waters which pass over it, but the rocks a short depth below 

 the surface are quite free from lime. 



With the exception of the region about Mossoro and Assu the 

 entire series of sedimentary rocks seems to be deposited in a fairly 

 even line down the coast, the belt always becoming a little narrower 

 toward the south. In the locality excepted there is a large basin 

 inland. This can readily be explained by the nature of the drainage 

 in that region. The three rivers Jaguaribe, ]\Iossor6 and Assu, are 

 the largest along this part of the coast, and although they drain a 

 large area their mouths are close together. Naturally in their im- 

 mediate vicinity erosion was deeper and more general than in areas 

 of lesser drainage. Hence, when the land sank the water was able 

 to reach much further inland in this vicinity than in any other along 

 the coast of Parahyba and Rio Grande do Norte, and the subsequent 

 deposition covered a correspondingly larger territory. 



Other than the sedimentary rocks along the coast there are several 

 areas of stratified rocks, smaller and completely isolated, in the states 

 of Parahyba and Rio Grande do Norte. Chief among these is the 

 sandstone basin of the Rio do Peixe. Beginning at the approximate 

 juncture of the Rio Piranhas with the Rio do Peixe and extending 



Fig. 4. Section across the sandstone basin of the Rio do Peixe, Parahyba. 



over the divide into the head waters of the Rio Pendencia, a distance 

 of 80 kilometers, there is a basin of reddish sandstone. The basin has 

 a varying width which averages between 9 and 12 kilometers for the 

 entire length, and has, moreover, a long arm which extends more 

 than 12 kilometers up to Belem. It is an isolated area of sandstone 

 in the midst of a vast stretch of crystalline rocks. The typical rock 

 is a reddish and rather fine-grained sandstone, which, in the upper 

 part of the basin, or roughly that part above Souza, is very common 



