BRANNER: THE STONE HEEFS OF BRAZIL. 99 



effectiveness is due to the coral reef that lies outside, however, and 

 greatly reduces the force of the surf that reaches it. At its southern end 

 it is split in two. South of this end and in a general line of the main reef 

 are five or six isolated rocks that are probably remnants of the reef in 

 that direction. North of the north end of the reef there is no flat land 

 on the beach, the cliffs coming close up to the water. There are no rocks 

 on the beach as shown on the hydrographic charts. 



The reef has the appearance of having been nearly everywhere more 

 or less cracked and these cracks filled with sand which is now hard like 

 the rest of the rock. In places the cracks have been washed open to a 

 depth of more than half a metre. The cracks run in every direction, 

 but the greater part of them are parallel with the reef. Along the sides 

 blocks from three to six metres long and from one to four metres across 

 have broken away from the main reefs on both sides and have sunk into 

 the sand and mud next to the reef. In some places the reef rock over- 

 hangs on the landward side where it seems to be undercut by the stream 

 or outflowing tide. 



North of the river the old town of Porto Seguro stands upon a plateau 

 forty-five metres high, and for the most part covered w'ith forest. 



The following description of this reef is given by Hartt, who examined 

 it in 1865:^ "The rock is obliquely laminated as in a sand beach, the 

 lamina dipping seawards at a small angle. It is composed of rather 

 fine sand, with occasional small pebbles, compactly held together by a 

 calcareous cement. It contains an abundance of recent shells, Venus, 

 Cerithium, Chama, etc., such as now live on the sea beaches of the 

 vicinity." 



There is, however, a marked diffei'ence between the rock of this reef 

 and that of the others. The sand is much whiter and, on the average, 

 coarser. Many of the pebbles are as large as pigeon's eggs, and the 

 fossil shells are moderately abundant. In one block I found a jDiece of 

 the coral Porites embedded in the reef rock. In places the reef rock is 

 exceedingly hard and breaks through the quartz grains with an almost 

 glassy fracture. 



My general impression of the Porto Seguro reef is that it is one of 

 the weakest of the Brazilian stone reefs. It is an important one because 

 it protects the port in the great Cabral Bay already partly pi-otected 

 by the great coral reefs outside. 



Notes upon little-knotvn stone reefs — The preceding detailed descrip- 

 tions of individual stone reefs contain all the notes made upon the reefs 



1 Geology and physical geography of Brazil, p. 229. 



