Northeast Coast of Brazil. 381 



Iron-Cemented Sandstone. 

 Cliffs. 



Practically the entire coast northward from Rio Grande to 

 Norte is bordered by the red and parti-colored sands and sandy 

 clays, probably of Tertiary age, which also border the coast for 

 many miles southward from that place. Along perhaps the 

 greater part of the coast to the north these colored sediments 

 are obscured by drifting beach sands, but in many places 

 they form cliffs which, though ordinarily less than 50 feet in 

 height, are prominent features of the low coast line. The 

 limestone which underlies these sediments and is exposed a 

 few miles inland, is seen near the beach at only two localities. 

 One locality is near Fazenda As Mocas, 25 miles east of Macau 

 and 1J miles from the beach, where a flat surface of hard, 

 gray, fossiliferous stone is exposed over an area several hun- 

 dred yards in diameter, beyond the extremity of a tidal inlet. 

 The other exposure is 8 miles farther west, in the channel of 

 another tidal inlet, at the base of a 1ow t bluff of the colored 

 sediments. 



In several places, notably at Tres Irmaos, the sedimentary 

 cliffs form headlands against which the surf beats, but in other 

 places they are not prominent features on the map. In the 

 reentrant a few miles northwest of Cabo Sao Roque, cliffs of 

 the red sediments rise from the surf to heights of 20 to 30 feet, 

 but at the cape itself there is no cliff. Large knolls of light- 

 colored sand, partly brnsh-covered, trend uniformly northwest 

 at this place, while the beach around the cape is protected by a 

 wide fringe reef of iron-cemented sand. The material of the 

 coastal cliffs varies in character from place to place and in the 

 several layers exposed in a single cliff. 1 ne various shades of 

 yellow and red-brown due to iron prevail, but in some places the 

 material has a mottled appearance caused by small patches of 

 white or pale-yellow sandy clay in the mass. It seemed to the 

 writer that the prevailing color of the cliffs north of Rio Grande 

 do Norte is considerably darker than is that of the cliffs south 

 of this port. It is worthy of especial note that no shales were 

 seen at any part of the coast north of Rio Grande do Norte, 

 though shales are found at numerous places farther south. 



The cliffs northwest of Cabo Sao Roque expose sections 

 approximately as shown in figure 8a and b, while a low cliff 

 22 miles in a direct line northwest of the cape, between the 

 villages of Peroaba and Carnaubinha, exposes cross-bedded 

 sands as shown in figure 8c. Other cliffs northward, notably 

 those at Touros, Ponta Reducto and Tres Irmaos, do not show 

 distinct beds, the material being consolidated as a whole with 

 only local differences in color, hardness and texture. These 



