218 Cruise of the "Alert" 



Porcellana, Atergitus, Sat/a, Alpheus, etc., and a large variety ot 

 Corals and Polyzoa. 



One of the most conspicuous objects about the foreshore at 

 Port Mahe is a curious fish of the genus Periophthalmus, which 

 may be seen not only jumping about the dry mud flats at low 

 water, but also climbing up the rugged vertical faces of the blocks 

 of granite of which the sea-wall and pier are formed. It is very 

 difficult indeed to catch one, as I have good reason to know. 

 Associated with them were several species of crabs, among which 

 I recognized representatives of the genera M r (xerophthalmus ', Gela- 

 sitniiS) Grapsus, and Ocypoda. 



The Seychelles are peculiar in being the only small tropical 

 oceanic islands of granitic structure. All the others, excepting 

 St. Paul's Rocks, are either of volcanic or coral formation. The 

 rock about Port Mahe is a syenitic granite, in which the mica of 

 ordinary granite is replaced by hornblende. In some cases the 

 felspar is coloured blue, in others reddish, and in every instance 

 it occurred in large coarse crystals. The soilcap was a reddish 

 pasty clay, of great thickness. In one of the road cuttings near 

 the settlement a section of this clay fully ten feet in depth was 

 exposed. 



We left Mahe on the 14th of March, and on the following day 

 anchored off a small coral islet, the northernmost of the Amirante 

 Group. This, with another similar islet adjoining, constitute the 

 African Islands. A party of surveyors immediately landed in 

 order to fix on a suitable place for taking midnight observations 

 of the stars, and I had soon afterwards an opportunity of landing 

 to explore. The islet is two hundred yards long, by about sixty 

 yards in width, is more or less elliptical in outline, low, and flat, 

 and for about three -fourths of its circumference is girt by a 

 smooth beach of coral sand, on the surface of which I noticed 

 a prodigious number of Orbitolites discs. The northern end of 

 the islet is composed of upraised coral sandstone, which has been 

 grooved and honeycombed into various fantastic shapes, so that 



