C(ELENTERATA 217 



Pacific Ocean are composed wholly of coral, and the 

 great barrier reef of Australia is also coralline. Many 

 rocks consist of fossil coral ; thus a fossil coral reef may 

 be seen at Beulah, New Mexico, now 8000 feet above the ' 

 level of the sea. Charles Darwin, during the voyage of Darwin's 

 the Beagle, studied the formation of coral reefs, and con- 

 cluded that the circular coral islands represented vol- 

 canic peaks or masses of rock which had disappeared 

 beneath the waves, leaving the surrounding coral to 

 grow upward in circular form. The coral animals do 

 best where the surf breaks on them, the water being 

 abundantly supplied with oxygen, and hence they tend 

 to grow most on the outer side of the reef. Were the 

 reef to subside suddenly, the animals would perish ; but 

 the subsidence has been so slow that they have kept pace 

 with it, building always on the skeletons of their ances- 

 tors. The wash of the waves has piled up masses of 

 dead coral, with the result of forming a beach a little 

 above sea level, on which coconut palms and other vege- 

 tation may grow. Professor W. M. Davis of Harvard 

 University recently visited the South Seas to study this 

 matter afresh, and was able to confirm Darwin's theory. 

 It must be said, however, that there are various kinds of 

 reefs, and some of them are largely due to lime-secret- 

 ing algae or seaweeds. 



