CORAL-REEFS. 107 



Keeling and other atolls, but compared with most coasts it 

 is steep. The water was so clear outside the reef, that I 

 could distinguish every object forming the rugged bottom. 

 In this part, and to a depth of eight fathoms, I sounded 

 repeatedly, and at each cast pounded the bottom with the 

 broad lead, nevertheless the arming invariably came up 

 perfectly clean, but deeply indented. From eight to fifteen 

 fathoms a little calcareous sand was occasionally brought 

 up, but more frequently the arming was simply indented. 

 In all this space the two Madrepores above mentioned, and 

 two species of Astraea, with rather large 1 stars, seemed the 

 commonest kinds ; and it must be noticed that twice at the 

 depth of fifteen fathoms, the arming was marked with a 

 clean impression of an Astrsea. Besides these lithophytes, 

 some fragments of the Millefiora alcicornis, which occurs in 

 the same relative position at Keeling Island, were brought 

 up ; and in the deeper parts there were large beds of a 

 Seriatopora, different from S. subulata, but closely allied to 

 it. On the beach within the reef, the rolled fragments 

 consisted chiefly of the corals just mentioned, and of a 



1 Since the preceding pages were printed off, I have received from 

 Mr. Lyell a very interesting pamphlet, entitled Remarks upon Coral 

 Formations, etc., by J. Couthouy, Boston, United States, 1842. 

 There is a statement (p. 6), on the authority of the Rev. J. Williams, 

 corroborating the remarks made by Ehrenberg and Lyell (p. 118 of 

 this volume), on the antiquity of certain individual corals in the Red 

 Sea and at Bermuda ; namely, that at Upolu, one of the Navigator 

 Islands, " particular clumps of coral are known to the fishermen by 

 name, derived from either some particular configuration or tradition 

 attached to them, and handed down from time immemorial." With 

 respect to the thickness of masses of coral-rock, it clearly appears, 

 from the descriptions given by Mr. Couthouy (pp. 34, 58), that Man- 

 gaia and Aurora Islands are upraised atolls, composed of coral rock: 

 the level summit of the former is about 300 feet, and that of Aurora 

 Island is 200 feet above the sea-level. 



