BIRD AND DENNIS ISLANDS, SEYCHELLES 



15 



C. BIRD AND DENNIS ISLANDS, SEYCHELLES. 



By J. C. F. Fryer, B.A., Research Student of Gonville and Cuius College, 



Cambridge. 



I. BIRD ISLAND. (Fig. 2.) 



Bird island, or He aux Vaches, is the most easterly of two small islands, which 

 are unique in being the only islands existing on the edge of the Seychelles bank. At 

 present the name " Bird island " is decidedly the most appropriate ; but formerly there 

 is no doubt the island was the haunt of the species of dugong known as Vache Marine, 

 which unfortunately has long ceased to exist. 



The island is small, having an extreme length of 1800 yards and width 1000 yards: 

 it is nearly uniform in level, the elevation above low water mark not exceeding 14 feet. 



The composition of the island appears to be entirely of calcareous sand, on the 

 top of which there was formerly 

 a layer of guano : the best of this 

 has, however, been removed and 

 the phosphate, which now exists, 

 is all in the form of a surface 

 stratum of soft sandstone. This 

 sandstone, which is very friable, 

 seems to have been largely formed 

 by the agglomeration of the 

 calcareous sand particles by means 

 of the phosphoric acid in the 

 guano. Underneath the surface 

 stratum, which is brown in colom', 

 is a white, calcareous sand, which 

 in most places has been formed into 

 a soft sandstone rock, this having 

 been effected partly perhaps by 

 phosphoric acid but mainly by lime 

 deposited from solution in rain- 

 water. No doubt in the more 

 superficial layers the phosphoric 

 acid is neutralised by the lime, 

 and the carbon dioxide produced, 

 remaining in solution, helps to dis- 

 solve more lime, which, redeposited 



at lower levels, serves to cement the sand particles together. No particular stratification 

 was observed in the sand, but all observations were made from pits or wells, and possibly 

 a long trench would furnish further details. In no part of the island was either any 

 plutonic or true reef rock observed, which might form a basis for the sand to collect on. 



Pig. 2. Bird Island. 



