56 LIFE OF 



the world than the originality of his views on coral reefs. 

 The lagoon islands, or atolls, he describes as " vast rings 

 of coral rock, often many leagues in diameter, here and 

 there surmounted by a low verdant island, with dazzling 

 white shores, bathed on the outside by the foaming 

 breakers of the ocean; and, on the inside, surrounding 

 a calm expanse of water which, from reflection, is of a 

 bright, but pale, green colour." Keeling atoll, outside 

 which, at less than a mile and a half distance, no bottom 

 was found with a line 7,200 feet in length, having been 

 fully described, and an account given of all other known 

 atoll systems, the peculiarities of the great barrier reef of 

 North-east Australia, and that of New Caledonia, were 

 recounted. Off the latter, no bottom was found, at two 

 ships' length from the reef, with a line 900 feet long. 

 With these were linked the smaller reefs of Tahiti and 

 others, where considerable islands are more or less com- 

 pletely surrounded by them. Next, the fringing or shore 

 reefs, at first sight only a variety of barrier reefs, were 

 clearly distinguished from them by the absence of an 

 interior deep-water channel, and their not growing up 

 from an immense, but from a moderate depth of 

 water. 



The remarkable fact was pointed out by Darwin that 

 all coral islands are within a little more than 30 degrees of 

 the Equator, but that, at the same time, they are absent 

 over certain larger areas within the tropical seas. There 

 are none on the West Coast of South America, nor on the 

 West Coast of Africa. In this portion of his work we 

 have another significant sentence bearing on the struggle 

 for existence. In discussing the apparently capricious 



