CAUSES INFLUENCING THE GROWTH OF CORAL ZOOPHYTES. 63 





Latitude. 



Depth of 6° ' 



Fahrenheit. 





15° 



. 



40—60 



fathoms. 





10° 



. 



50—75 



(i 





5° 



. 



75 



u 



Equator. 



0° 



- 



75— 10C 



" 



S. Latitude. 



5° 



. 



50—75 



u 





10° 



. 



50 



It 





15° 



- 



50 



u 





20° 



. 



40 



u 





25° 



. 



25 



it 





28°- 



-30° 



Surface. 





It appears, therefore, that among the causes limiting the range 

 of corals in depth, light and hydraulic pressure must have great 

 influence. The proportion of atmospheric air present may be 

 another cause. Yet according to Darondeau, the deeper waters 

 contain more atmospheric air and also more carbonic acid, — the 

 difference being as much as T 'oth the volume of the water.* 



Q,uoy and Gaymard were the first authors who ascertained that 

 reef-forming corals were confined to small depths, contrary to the 

 account of Forster and the early navigators. The mistake of 

 previous voyagers was a natural one, for coral reefs were proved 

 to stand in an unfathomable ocean ; yet it was from the first a 

 mere opinion, as the fact of corals growing at such depths had 

 never been ascertained. It is now considered altogether probable 

 that the bottom of the ocean in its deeper parts is mostly without 

 life of any kind. The few Caryophylliae and other species which 

 are met with in deep waters, have been shown to be sparsely 

 scattered, mostly of small size, and nowhere form accumulations 

 or beds. 



The above-mentioned authors, who explored the Pacific in the 

 Uranie under D'Urville,f concluded from their observations that 

 five or six fathoms (30 or 36 feet) limited their downward dis- 

 tribution. Ehrenberg, by his observations on the reefs of the 

 Red Sea, confirmed the observations of Q,uoy and Gaymard ; he 

 concluded that living corals do not occur beyond six fathoms. 

 Mr. Stutchbury, after a visit to some of the Paumotus and Tahiti, 

 remarks that the living clumps do not rise from a greater depth 

 than 16 or 17 fathoms.}: Mr. Darwin, who traversed the Pacific 

 with Captain Fitzroy, R. N., gives 20 fathoms as not too great a 

 range, and mentions reported instances of growing reefs in 25 or 

 even 30 fathoms. He states that in the Red Sea, according to 

 Captain Morehead, living corals occur at 25 fathoms. At Keel- 

 ing Atoll, growing corals are described by him as wholly disap- 



* Examination of Sea Water collected during the Voyage of the Bonite, Jame- 

 son's Edinb. Jour., July, 1838, p. 164. Darondeau's observations require confirmation, 

 f Afterwards also in the Astrolabe. 

 \ S. Stutchbury, West of England Journal, i, 48. 



