Northeast Coast of Brazil. 



371 



together with the representation of this reef on Plate IX, it 

 well brings out two characteristics of the better-developed 

 reefs, i. e., their relations to present beach lines, and their posi- 

 tions relative to stream mouths. 



North of Rio Grande do Norte the first typical calcareous 

 sandstone was found at the mouth of Rio Ceara-Mirim, where 

 a double reef of the material is exposed at low tide (fig. 2). 

 The two reefs are parallel, about 100 yards apart and curve 



Fig. 1. 



Fig. 1. Reef at moutli of Rio Grande do Norte. 



gently with the present beach. The inner reef is the shorter, 

 and some parts of it project only a few inches above the sand 

 of the flat beach that is laid bare by the receding tide. Its 

 rock is brighter in color and softer than the usual pale yellow 

 to gray material, but otherwise it has the appearance of the 

 typical reef rock. It is the most probable example noted of a 

 recently formed deposit. A tidal lagoon, fringed with man- 

 grove, is formed behind a bar which separates it from the 

 beach. The outer reef consists of the usual hard, gray 

 material. About 450 yards beyond the place where its north- 

 ern end disappears beneath the water, another stretch of the 

 same material, probably its continuation, appears close to the 

 shore and extends around a gently curving beach, gradually 

 receding and disappearing beyond the surf. 



Proceeding northward, the reef rock next appears as a few 

 scattered blocks in the surf about one mile south of a low point 

 near the village of Pitangy. About 500 yards beyond these 

 blocks, the material is exposed as a continuous reef, with bed- 



