CORAL REEFS OF TORRES STRAITS 215 



in a manner quite different from that of the recent fringing reefs of the 

 Murray Islands. According to these students water was abstracted from 

 the sea to form the great polar ice caps of the glacial epoch, and Pro- 

 fessor R. S. "Woodward has demonstrated mathematically that a still 

 further lowering of level in tropical seas must have resulted from the 

 attraction of the ice caps for the ocean surrounding them. 



Thus the level of the tropical oceans may have been about 120 feet 

 lower than at present. Now under these conditions the oceans would 

 wash away the shores forming platforms along the tropical coasts at a 

 level which would be about 120 feet below the present surface of the 

 water. 



Then when the ocean began again to rise, after the close of the 

 glacial epoch, corals would grow along the outer edges of these platforms 

 and thus Atolls and Barrier Reefs have been formed ; the Atolls growing 

 upon the truncated summits of mountains. 



Andrews called attention to the fact that the platform upon the 

 outer edge of which the Great Barrier Reef has grown, extends south- 

 ward far beyond the latitude of corals, and Vaughan has observed that 

 the platform of the Florida reef extends far northward beyond the last 

 coral reefs. Also we may observe the Barrier Reef platform extends 

 northward to the coast of New Guinea although the corals are killed in 

 the wide region of the Bligh Entrance by the silt of the Fly and other 

 great Papuan rivers. Thus it appears that the corals have merely 

 grown as break-waters upon the seaward edges of platforms which were 

 formed before the reefs themselves developed. 



In some respects, the Pacific reefs are markedly different from those 

 of the Atlantic. In the Pacific, one misses the beautiful sea fans and 

 gorgonians that wave in languid grace to the rhythm of the surges in 

 the crystal waters of Florida and the Bahamas. Instead, we find large 

 areas of leathery-looking alcyonaria, or fleshy eight-rayed corals, 

 Sarcopliyton and Alcyonium, and in the crevices one often sees the 

 giant clams Tridacna, their valves opened to show the beautiful mantle 

 edges of malachite green, or blue, yellow or mottled with brown in a 

 gamut of color, no two individuals being alike. 



There are almost twice as many kinds of corals in the Pacific as 

 in the Atlantic, and some of the more fragile of these grow luxuriantly 

 down to depths of 60 feet or more, whereas in the Atlantic the coral 

 reefs thrive well only in shallow water not over 20 feet in depth. 



But the most striking feature which distinguishes the Pacific reefs 

 is the development of a ridge which actually projects half a foot or 

 more above low tide level and extends along the outer seaward edge of 

 the reef-wall wherever the breakers dash. In the Paumotos, this ridge 

 is dull reddish pink in color, and it is composed of a mass of stony 

 seaweeds or nullipores of the sort called Lithothamnion, and also of 



