MANNER OF FORMATION 

 OF CORAL REEFS 



ALL CORAL REEFS are built in a similar manner, 

 by the growth and accumulation of stony 

 skeletons of the coral animal, but they are 

 not by any means the same in general 

 appearance and structure. There are^ in 

 fact, three main types of reef. The kind known as a 

 fringing reef is found quite close to the shores of con- 

 tinents or rocky islands in shallow water. In contrast 

 to this a barrier reef is usually separated from the shores 

 of the mainland by a channel many miles wide and as 

 great as 175 feet in depth. The third type, known as 

 an atoll is not connected with any land mass but rises 

 to the surface as a low\island, roughly ring-shaped and 

 surrounded by water several thousand feet deep. 



The fringing reef is formed by corals growing close 

 to the shore in shallow water. As they increase in size 

 and number they grow towards the surface and also 

 outwards in the direction of the open ocean. This is a 

 consequence of previously mentioned living require- 

 ments of the reef corals, which flourish at their best 

 where wave action is strong. Similarly the corals be- 

 tween the outer edge of the reef and the shore tend to 

 die as a result of increased temperature and salinity 

 changes, and of deposition of sediment. The net result 

 of growth at the outer edge of the reef is shown in 

 figure 2. A broad platform of partly living and partly 

 dead coral rock is formed, extending horizontally from 

 the shore. At the outer edge is the living and actively 



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