branxer: the stone reefs of brazil. 



161 



uncovered by the shifting of the currents. The coral reef surfaces are 

 usually so blackened with corallines and other growths that the struc- 

 ture cannot be seen, but at this place it is shown perfectly. Heads of 

 Porites and other corals are cut through and partly eaten away either 

 chemically or mechanically. At low tide these reefs- are exposed for 

 half a kilometre out seaward. Nearly one kilometre south of the beach 

 exposure just mentioned is another place where the beach sands overlie 

 a dead coral reef. The photograph given herewith was taken at the 

 last-named place. It shows not only the in-shore reef but two other 

 coral reefs further out : the further of these is nearly one kilometre from 

 the shore. 





Fig. 89. High Rock, Maceio coral reef. From a photograpli by F. Ambler. 



In this connection mention should be made of a ma.=^s of coral rock on 

 the reef at Maceio. The Maceio reef is of coral, is three kilometres or 

 more in length, and varies in width from a few paces at certain points 

 to nearly a kilometre at its northern end, where it joins the sandy beach. 

 At one point east of Jaragua. a solitary mass of coral rock rises three 

 metres above the general level of the coral reefs. Tliere is no other 

 such rock on the Maceio reefs. It was formerly supposed that this was 

 the remnant of an old reef that had been cut away by the waves. The 

 accompanying illustration made from a photograph kindly obtained for 

 me by Mr. F. Ambler of the Alagoas Railway Company at Maceio shows 

 that tliis mass is simply a tilted fragment of the reef thrown into its 

 present position by having been undermined at one end. 



VOL. XLIV. 



11 



