BRANNER: THE STONE REEFS OF BRAZIL. 67 



As elsewhere pointed out, I regard the clays found in the lower 

 portions of these reef sections as evidence of the present beach line, 

 and of the reef itself having been formed against or deposited upon an 

 older beach that formerly lay further landward. The clays themselves 

 are not beach deposits, but are the ofF-shore equivalents of beach 

 sands. 



That these stone reefs should have withstood the seas that break upon 

 and over them, especially during heavy southeast gales, is one of the 

 remarkable things about them, and especially so when we remember 

 that only the upper part of the reef is consolidated. It is worthy of 

 note also that when the reef is broken up the breaking seems to be due 

 largely to the attack upon its landward side rather than to the force of 

 the waves that break upon it from the sea. 



At one place the force of the stream discharged into the harbor, and 

 against the landward face of the Pernambuco reef, probably aided by the 

 nature of the water, has undermined the reef. This is a common feature 

 of the stone reefs all along the Brazilian coast, and is due in part to the 

 fact that only the upper part of the reef is thoroughly consolidated. 



In some places this kind of undermining has led to the breaking up of 

 the reef, and the surface blocks now lie strewn upon the bottom or tipped 

 about in confusion. 



The fact that the outer face of the reef is not attacked more vigor- 

 ously by waves is due to the protection afforded by the great quantities 

 of Serpulae, barnacles, seaweeds, and the like that coat its outer surface. 



Tlie beach reef at Piedade. — Following southward along the beach 

 from the southern end of the Pernambuco reef at Boa Viagem by the 

 sea one has on the land side a low ridge of sand some four metres high 

 — the continuation of tliat at Boa Viagem — and behind this the fresh- 

 water marshes and Lake Curcurana. The topographic surroundings are 

 therefore very much the same as those about the southern end of the 

 Pernambuco reef. 



The first signs of a stone reef in this direction are at the Piedade 

 church, less than a mile south of Boa Viagem. At this place there is a 

 small beach reef about a hundred metres long. The rock is quite hard, 

 but not flinty, and is of the same yellowish color as the beach sands. 

 Its surface is etched in holes and overgrown with a thin coat of green 

 seaweeds. 



The seaward dip of these rocks is clearly shown, and the following 

 angles were noted : 4^°, 5°, 6°, 6^°. The following dips of the beach 

 sands alongside were noted : 4°, 4|°, 5°. 



