CORAL-REEFS. 125 



of Capt. Beechey's. Whitsunday Island is described by 

 Wallis as "about four miles long, and three wide," now it 

 is only one mile and a half long. The appearance of 

 Gloucester Island, in Capt. Beechey's words, 1 "has been 

 accurately described by its discoverer, but its present form 

 and extent differ materially." Blenheim reef, in the Chagos 

 group, consists of a water-washed annular reef, thirteen 

 miles in circumference, surrounding a lagoon ten fathoms 

 deep : on its surface there were a few worn patches of 

 conglomerate coral-rock, of about the size of hovels ; and 

 these Capt. Moresby considered as being, without doubt, 

 the last remnants of islets ; so that here an atoll has been 

 converted into an atoll-formed reef. The inhabitants of the 

 Maldiva Archipelago, as long ago as 1605, declared, "that 

 the high tides and violent currents were diminishing the 

 number of the islands :" 2 and I have already shown, on the 

 authority of Capt. Moresby, that the work of destruction is 

 still in progress ; but that on the other hand the first 

 formation of some islets is known to the present inhabitants. 

 In such cases, it would be exceedingly difficult to detect 

 a gradual subsidence of the foundation, on which these 

 mutable structures rest. 



Some of the archipelagoes of low coral-islands are subject 

 to earthquakes : Capt. Moresby informs me that they are 

 frequent, though not very strong, in the Chagos group, 

 which occupies a very central position in the Indian Ocean, 

 and is far from any land not of coral formation. One of 

 the islands in this group was formerly covered by a bed of 

 mould, which, after an earthquake, disappeared, and was 



1 Beechey's Voyage to the Pacific ; chap, vii., and Wallis's Voyage in 

 the Dolphin, chap. iv. 



2 See an extract from Pyrard's Voyage in Captain Owen's paper on 

 the Maldiva Archipelago, in the Geographical Journal^ vol. ii. p. 84. 



