70 



BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



the bay, another about one third, and the other two thirds of the way 



from Gaibu to Pedras Pretas. 



Lying along the beach of Gaibu Bay, but here and there a httle way 



out from it, is a sandstone reef ex- 

 tending nearly all the way from 

 Pedras Pretas to the edge of the 

 village of Gaibu. It is three kilo- 

 metres or moi*e in length and 

 varies in width from forty-five to 

 two hundred and forty metres, — 

 a remarkable width for a stone 

 reef. At low tide it stands two 

 metres out of water at its highest 

 points. It has a gentle seaward 

 dip. The rock is of the ordinary 

 sugar-brown sandstone and con- 

 tains an abundance of fossil marine 

 shells. The surface has the etched 

 appearance so characteristic of the 

 stone reefs. 



The accompanying photograph 

 Fig. 37. Gaibu Bay. ^p^^^^ ^^^ ^^^^^^ ^^^^^ ^j^^ ^^.^^^j^^ 



hills south of the bay shows the southern end of this beach reef. 



Fig. 38. Plan of a miniature bay behind a break in the Gaibu reef. 



South of the middle of this reef is a small break through which the 

 waves have been able to encroach upon the beach and to form a minia- 

 ture bay protected by the ends of the stone reef. 



