the lagoon channel, which is dotted with scattered heads 

 of coral. These heads are more scarce towards land, 

 where the effects of fresh water drainage and sediment 

 become more pronounced. The more exposed parts of 

 the mainland and of islands within the lagoon channel 

 may acquire fringing reefs. Small islands may appear 

 on the reef itself where they are gradually formed by 

 the accumulation of dead coral and silt and where 

 finally, as sand accumulates, palm trees and mangroves 

 may develop from seeds washed ashore. 



The foregoing brief and simplified description of the 

 Great Barrier Reef applies in a general way to all 

 barrier reefs. These are found in the Pacific among the 

 Society Islands, the Fiji Islands, New Caledonia and to 

 the southeast of New Guinea, but are unusual in the 

 Atlantic Ocean and only appear to a limited extent in 

 the Indian Ocean. 



Atolls are in some ways the most interesting of reef 

 formations. They are the true coral islands of romantic 

 fiction as well as of scientific texts. Far from any main- 

 land they are like oases on the surface of the ocean, 

 arising as if by magic in water thousands of feet deep. 

 Graceful palm trees grow on the fringe of the quiet 

 waters of their protected lagoons where an abundant 

 supply of seafood awaits the hungry castaway. Atolls 

 are no less intriguing to the scientist since they offer 

 a diversity of interesting problems, in their structure 

 and mode of formation. The coral reef of an atoll is 

 essentially the same as a barrier reef or fringing reef, 

 but differs in being roughly ring-shaped, with steep 

 outer sides sloping down into very deep water. Inside 

 the encircling ring of reefs is a shallow lagoon which 

 is rarely 1 00 feet deep (see figures 5 and 6) . The lee- 



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