38 CORAL-REEFS, 



reef, has been noticed by several authors. There are some 

 atoll-formed reefs, rising to the surface of the sea and 

 partly dry at low water, on which from some cause islets 

 have never been formed ; and there are others on which 

 they have been formed, but have subsequently been worn 

 away. In atolls of small dimensions the islets frequently 

 become united into a single horse-shoe or ring-formed 

 strip ; but Diego Garcia, although an atoll of considerable 

 size, being thirteen miles and a half in length, has its lagoon 

 entirely surrounded, except at the northern end, by a belt 

 of land, on an average a third of a mile in width. To show 

 how small the total area of the annular reef and the land 

 is in islands of this class, I may quote a remark from the 

 voyage of Lutke, namely, that if the forty-three rings, or 

 atolls, in the Caroline Archipelago, were put one within 

 another, and over a steeple in the centre of St Petersburg, 

 the whole world would not cover that city and its suburbs. 



The form of the bottom off Keeling atoll, which gradually 

 slopes to about twenty fathoms at the distance of between one 

 and two hundred yards from the edge of the reef, and then 

 plunges at an angle of 45 into unfathomable depths, is 

 exactly the same 1 with that of the sections of the atolls in 

 the Low Archipelago given by Captain Beechey. The 

 nature, however, of the bottom seems to differ, for this officer 2 

 informs me that all the soundings, even the deepest, were 

 on coral, but he does not know whether dead or alive. 



1 The form of the bottom round the Marshall atolls in the Northern 

 Pacific is probably similar: Kotzebue {First Voyage, vol. ii. p. 16) says: 

 " We had at a small distance from the reef, forty fathoms depth, which 

 increased a little further so much that we could find no bottom." 



2 I must be permitted to express my obligation to Captain Beechey, 

 for the very kind manner in which he has given me information on 

 several points, and to own the great assistance I have derived from his 

 excellent published work. 



