492 EVOLUTION OF ANIMALS Part V 



the land had sunk creating wide channels and barrier reefs; that in the case of 

 islands the land might have sunk completely out of sight and formed the 

 lagoon. The relatively recent Glacial-control Theory states: that during the 

 last glacial period the amount of water frozen in the great ice caps may have 

 lowered the ocean by about 200 feet. Shallows resulted covering many plat- 

 forms of the ocean with water too cold for corals. However, as the ice melted 

 and the waters were warmed coral growth began and kept pace with the rising 

 ocean level. This theory accounts for the uniform depths of coral lagoons 

 whose bottoms may represent the platforms which existed when the ocean was 

 at its ancient low level. 



Attempts to unravel the mystery of reef formation have been made by bor- 

 ing deep into a reef and identifying the coral skeletons found at low levels. 

 This was done on Funafuti Atoll, in the South Pacific north of Fiji. One boring 

 about five inches in diameter was carried down 1114 feet without reaching 

 the base of the reef. Twenty-eight reef-building corals were identified and of 

 these 22 are now living on the reef in water around 100 feet deep. Borings on 

 other reefs have given similar results, all of them supporting the glacial-control 

 theory. 



