BRANNER : THE STONE REEFS OF BRAZIL. 159 



simply an inference based upon tlie supposition that these organisms 

 would affect the rock along the line where they grow. 



2. Elevated seorurchin hurroius. — The boring sea-urchins of this coast 

 {Echinometra subangularis) can live in places where at low tide the 

 waves break over them occasionally, or they can live in tide-pools. But 

 so far as I can learn they do not live in places where they are completely 

 uncovei'ed at low tide. 



A few kilometres north of Cabo Santo Agostinho, at a point of land 

 known as Pedras Pretas are many exposures of a massive black trachyte 

 upon the sea beach and rising in the hills above. There are three or 

 more places where these trachyte masses in place are bored by sea-urchins. 

 These rocks, and one other and larger exposure, are in place, while a 

 third one may possibly be a loose block. The parts bored with these 

 holes are bet/ceen high and low tide leveU. As will be seen from the illus- 

 tration the exposures of these bored faces are such that it does not seem 

 possible that sea-nrchins could live in them if uncovered even at low tide. 



Of the several exposures of such borings at this Cape not one is found 

 beyond the reach of high tide. To put these holes all below low tide 

 would require a depression of two metres. 



It should be added that no such holes were found in the granites 

 exposed at Pedra do Porto and Pedra do Conde in the southern part of 

 the State of Pernambuco a short way north of Rio Una, but on Cabo 

 Santo ALTOstinho on the south side of the Cape and west of the sand 

 reef thei'e are a few holes in the granites between tide-levels that look 

 as if they might have been made or partly made by sea-urchins. 



3. TJie death and decay of the coral reefs. — The decay and erosion of 

 the upper surface of the stone reefs I have not seen mentioned as evidence 

 of elevation. The illustration given herewith shows a characteristic fan- 

 tastic form common upon the stone reefs of the coast. These forms have 

 the bedding of the original sand layers distinctly preserved and there 

 can be no question about their being the remnants of upper beds that 

 have been removed by erosion. This erosion, however, may have been 

 produced either by the ordinary processes of weathering and removal by 

 the waves, or it may have been the work of the surf. The form here 

 represented is still quite within the reach of the surf at high tide. These 

 forms cannot therefore be accepted as evidence of elevation. I do not, 

 however, feel so confident in regard to the meaning of the decay of the 

 upper portion of the coral reefs of the coast. I know of no reason why 

 the stone reefs may not have been consolidated at any elevation at which 

 they are now found. But in the case of the coral reefs the rock can be 



