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BRANNER: THE STONE REEFS OF BRAZIL. 109 
each other. The composition is treated under the head of “ Consolida- 
tion” in Part VI. 
The structure of a stone reef in cross-section is well shown in the 
accompanying figure, which was first published by Hartt in 1870. 
Sea 
Low Water 
Fria. 65. Theoretic section across a stone reef. — Hartt. 
The same structure is shown in Wagoner’s section of the Porto Seguro 
reef. (See p. 96.) 
In the undisturbed rocks the dip is almost invariably seaward, and 
the angles are the low angles common to beach sands. I have often 
measured the slopes of the beaches, and in а few instances I have been 
able to measure the dips of the reef rocks. At Piedade, a village on 
the coast a few kilometres south of Pernambuco, the rocks of the stone 
reef dip at angles varying between 44 and 64 degrees; the beach sands 
at the same place dip at angles varying between four and five degrees. 
At Venda Grande, just south of Piedade, the beach has a slope from 
four to five degrees. I have measured sand slopes as high as 37°, but 
these were cases of false bedding. The steepest beach noted on which 
the waves played was at the mouth of Rio Sapucahy, where it had a 
slope of 11°. 
At Pedras Pretas, the small cape just north of Cabo Santo Agostinho, 
a small stone reef has dips varying between five and eight degrees. The 
beach sands have similar dips. The stone reef of Pratagy shows its 
seaward dip well, but no angles were measured. Some of the photo- 
graphs of the Mamanguape reef also show the seaward dip of the rocks. 
Occasionally one sees strongly marked false bedding in the reef rocks. 
Cases of the kind have been noted on the Mamanguape reef. At Rio 
Grande do Norte the reef, as seen from the lighthouse on the reef, shows 
the beach structure fairly well. 
Mention should be made here of the statements of Liais that the reef 
rocks are sometimes vertical. As pointed out in Part V., no cases are 
known to the writer in which the reef rocks are vertical or have very 
high dips except where certain blocks have undermined and have 
tipped up on one side. 
