348 On Coral Reefs and Islands. 
\ The islands of the Indian Ocean-are, to a great extent, purely 
coral. Of this character are the Laccadives, Maldives, Keel- 
ings, Saya-de-Malha, Almirante, and Cosmoledo. 'The Chagos 
shoal is of the same character: and the shoal Cargados is proba- 
bly similar. The Seychelles are small islands with extensive 
reef; e remark here the same fact alluded to above, that 
reefs abound in the open ocean, though absent from the Conti- 
nental coasts; and the same reason may apply to both cases. 
Madagascar has a fringing reef upon its southwestern point, 
according to Mr. Darwin, and on some parts of the coast above; 
also on the north and eastern shores far down as latitude 18° S.* 
The Comoro Islands, between Madagascar and the continent, 
have large barrier reefs. 
The eastern coast of Africa has narrow reefs extending north 
with some interruptions from Mozambique, in latitude 16° S., to 
a short distance from the equator. Corals also abound in the 
Red Sea, occurring in some parts on both shores, though most 
frequent on the eastern, from Tor, in the Gulf of Suez, to Kon- 
fodah. This long continental reef may at first be deemed a little 
remarkable, after what we have remarked upon such reefs else- 
where. Yet the surprise is at once set aside by the striking fact 
that this whole coast, from the isthmus of Suez south, has no 
rivers, excepting some inconsiderable streams. It affords, there- 
fore, an interesting elucidation of the subject under consideration, 
and confirms the view taken to account for the absence of reefs 
, must 
have been formerly bordered by growing coral, as Quoy and 
aymard mention that a bed of coral rock may be seen buried 
beneath streams of lava, Quoy also states that the corals which 
formed these reefs are no longer found alive, and adds that vol- 
canic eruptions: have probably destroyed them. The cold polar 
currents along the Aftican coast, although generally leaving about 
fifteen degrees of latitude Within the -coral-reef may at 
? 
ring in the Pacific—that is, westerly currents—exists also in the 
Atlantic, and probably with the same effect, " 
* Darwin, >. cit., p, 187, : 
t Journal of the Royal Geographical Society, ii, 89. 
