*^sli 





■4 



1 «rV, 



•^O 



Arabi 



rt*. 



i^^^vt. 



■v. 





crs 



'^ Hollar^ • 

 ^ being i 



e 



in or 



groups (if 



1.-= ' miles i 



11 



^1 



•1 



400 1 



DanjerC':; 



. r 



mple. 



.J 



U-A--* 



. ■ 4iiids wife 



1 



^t 



, :"• -^n veiT 



tliiiilf 







0iaii 



t of tb? I"' 



'O 



flilsm 



itlatio" 



nJaii^ 



are 



■ : of ^^^ 



*0 







^ n^ 



'i 



r 



I 



Ch. XLIX.] 



RATE OF THE GROWTH OF CORAL. 



581 



in 



Millep 



10 to 20 feet tlie species of Dichocoenia, Stepliaiiocoenia, 

 and Desmopliyllum flourish. 



The distribution of particular species, in regard to the 

 depth of water in which they grow, is remarkably uniform. 

 According to Mr. Darwin, as will appear in the sequel, the 

 reef-building corals rarely live at a depth exceeding 120 feet, 

 but M. Duchassaing. obtained some species of stony corals 

 at depths of from 600 to 900 feet in the Caribbean Sea. In 

 temperate climates such species as the Garyophyllia SmytM, 

 Stokes, are sub-littoral ; but Dr. Duncan reminds 

 the fact is of no small geological significance, when we are 



that the closely allied species 



me 



on extinct forms, that the 

 G. horealis now lives in deep water off the Shetlands. 



Of the numerous zoophytes which are engaged in the 

 production of coral banks, some of the most common belong 

 to the Lamarckian genera Astrsea, Porites, Madrepora, 

 Millepora, Pocillopora, and Ma3andrina. 



)/ the groivth of 



— Very different opinions have 



been entertained in regard to the rate at which coral reefs 

 increase. In Captain Beechey's late expedition to the Pacific, 

 no positive information could be obtained of any channel 

 having been filled up within a given period ; and it seems 

 established, that several reefs had remained for more than 

 half a century at about the same depth from the surface. 



Ehrenberg also questions the fact of channels and harbours 

 having been closed up in the Eed Sea by the rapid increase 

 of coral limestone. He supposes the notion to have arisen 

 from tlie circumstance of havens having been occasionally 

 filled np in some places with coral sanely in others with large 

 quantities of ballast of coral rock thrown down from vessels. 



The natives of the Bermuda Islands point out certain corals 

 noAV grooving in the sea, which, according to tradition, have 

 been living in the same spots for centuries. It is supposed 

 that some of them may vie in age with the most ancient trees 

 of Europe. Ehrenberg also observed single corals of tlie 

 genera Mseandrina and Favia, having a globular form, from 

 6 to 9 feet in diameter, Svhich must (he says) be of 



