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bulletin: museum of comparative zoology. 



South of Barra Grande the line of coral reefs continues with "breaks to 

 tlie^ Porto de Pedras at the mouth of Eio Manguaba. South of that 

 place they are almost continuous to the mouth of Rio Camaragibe, — a 

 distance of twenty-four kilometres. The seaward face of this reef aver- 

 ages something more than a kilometre off the shore. 



At the Barreira do Boqueirao an inner reef, having its northern end 

 well off shore, swings round and comes squarely against the beach at its 

 south end, the beach sands lying on top of the dead coral reef. 



At Sao Miguel dos Milagres (S. lat. 9° 18' 30") the coral reef is 

 rather closer to the shore than usual. One kilometre south of there a 



coral reef is uncovered 

 on shore for a short dis- 

 tance; its south end 

 swings outward away 

 from the beach into deep 

 water. 



Three kilometres 

 south of Sao Miguel 

 there is a coral reef un- 

 covered on the beach at 

 the mouth of a small 

 stream. This piece of 

 reef has been dead for a 

 long while. Its surface 

 has been pitted and 

 worn by waves and sand, 

 then buried beneath the 

 encroaching beach sands, and now again it has been partly uncovered 

 by the shifting currents. The freshly uncovered surface shows the com- 

 position of the I'eef much better than it can be seen upon the ordinary 

 dead or even upon living reefs. The rock is mostly coralline and most 

 of the coral imbedded in this mass is Porites. The Porites form less 

 than half of the rock, — perhaps a third of it. 



This piece of reef runs out more than one hundred metres from the 

 shore at mean tide, and at low tide a width of nearly five hundred metres 

 is exposed. 



One kilometre south of this exposure the sand flats exposed at low 

 tide connect with and overlie the offshore dead coral reefs. The dead 

 reef is exposed along the beach for more than two kilometres, and the 

 water between it and the main reef outside (seaward) is very shallow 

 and full of coral rock. 



Fig. 97. Map showing positions of two coral reefs 

 near Silo Miguel ; the reef on shore is dead and 

 is partly covered by sand. 



