CORAL-REEFS. 87 



another : thus, the Pacific or Indian Ocean might become 

 as barren of coral-reefs as the Atlantic now is, without 

 our being able to assign any adequate cause for such a 

 change. 



It has been a question with some naturalists, which part 

 of a reef is most favourable to the growth of coral. The 

 great mounds of living Pontes and of Millepora round 

 Keeling atoll occur exclusively on the extreme verge of 

 the reef, which is washed by a constant succession of 

 breakers ; and living coral nowhere else forms solid masses. 

 At the Marshall islands the larger kinds of coral (chiefly 

 species of Astrsea, a genus closely allied to Porites) "which 

 form rocks measuring several fathoms in thickness," prefer, 

 according to Chamisso, 1 the most violent surf. I have 

 stated that the outer margin of the Maldiva atolls consists 

 of living corals (some of which, if not all, are of the same 

 species with those at Keeling atoll), and here the surf is so 

 tremendous, that even large ships have been thrown, by a 

 single heave of the sea, high and dry on the reef, all on 

 board thus escaping with their lives. 



Ehrenberg 2 remarks, that in the Red Sea the strongest 

 corals live on the outer reefs, and appear to love the surf; 

 he adds, that the more branched kinds abound a little way 

 within, but that even these in still more protected places 

 become smaller. Many other facts having a similar tend- 

 ency might be adduced. 3 It. has, however, been doubted 



1 Kotzebue's First Voyage (Eng. Trans.), vol. iii. pp. 142, 143, 331. 



2 Ehrenberg, titer die Natur und Bildung der Corailen B'dnke im 

 rothen Meere> p. 49. 



3 In the West Indies, as I am informed by Capt. Bird Allen, R.M., 

 it is the common belief of those, who are best acquainted with the reefs, 

 that the coral flourishes most, where freely exposed to the swell of the 

 open sea. 



