68 THE STORY OF LIFE IN THE SEAS. 



be thought that a rich profit could be gained by 

 collecting ship-loads of the Coral that is used for 

 making beads and brooches by our jewellers. 

 Any expedition, however, fitted out for this pur- 

 pose would end in disastrous failure, for the 

 Precious-coral is not known to occur anywhere 

 in the neighbourhood of Coral-reefs, but the 

 fishery is confined to certain parts of the Medi- 

 terranean Sea. Species closely allied to the 

 Precious-coral, but of an inferior colour, have 

 been found in the Japanese waters. None of 

 the Coral structures found on the reefs have the 

 same delicate salmon-pink colour and probably 

 none of them are hard enough to take a good 

 polish. 



The Coral-reefs which occur in different parts 

 of the Tropical world were considered by Darwin 

 under three heads, Barrier-reefs, Atolls, and 

 Fringing-reefs. The distinction between these 

 three kinds of reef is not one that can be insisted 

 upon scientifically, but the arrangement is con- 

 venient for purposes of description. 



The Barrier-reefs (Fig. 23, B) are situated at a 

 distance of one to eight miles from the coast, and 

 are separated from it by a lagoon of moderately 

 deep water. The Barrier-reef of New Caledonia \ 

 is said to be 400 miles in length and it follows 

 the general contour of the coast-line. 



The Atolls (Fig. 23, C) are ring-shaped islands 

 composed of coral limestone with a lagoon of salt i 

 water within them, situated in the sea without i 

 any definite relation to other existing land. 



The Fringing or shore-reefs (Fig. 23, A} are 4 

 situated at a distance of 100 yards or less from i 



