502 Mr Gardiner, The Coral Reefs of [Mar. 7, 



question Prof. Hartley says 1 : — "The penetration of light to the 

 bottom of the deep sea is a possible, if not a probable, phenomenon. 

 It is true that in the clear waters of Lake Leman photographic 

 plates are affected at mid-day at no depth beyond 120 fathoms; 

 but Messrs Fol and Sarasin 2 are led to suppose that the greater 

 transparency of sea water will admit of the extreme limit of 

 luminous rays reaching a still lower level. We have accordingly 

 no grounds for the conclusion that because chlorophyll has been 

 found at a depth of 553 fathoms, even if the pigment be produced 

 in situ, therefore light has not penetrated so far and has not 

 operated in its formation." I do not wish to contend that the 

 bathymetrical limit of nullipore life is to be placed at so great 

 depth, but that these algse grow down to 75 fathoms was shown 

 by one of the dredgings made by the Penguin to that depth. 

 The rate of growth of all algse depends largely on the strength of 

 the light, for on it their power of absorbing carbonic acid gas, 

 and giving off oxygen directly depends. Light also is probably 

 an extremely important factor to many reef-building genera of 

 corals. 



I can add nothing fresh to Murray's account of the methods 

 by which mounds can be built up to the requisite depth, what- 

 ever that may be, but I would call attention to the fact that 

 the growth of corals especially contribute towards this. The 

 evidence, so far as it goes, shows that animals in the sea have 

 a tendency to collect especially on any mounds ; and I do not 

 suppose that corals are any exception to this rule. In his report 3 

 on Madreporaria obtained during the expeditions of H.M. ships 

 Porcupine and Lightning, Martin Duncan noted " that the growth 

 of deep sea corals is very vigorous at great depths and at low 

 temperatures," and "that the present deep sea faunas contain 

 species and varieties of species of the Pliocene, Miocene and 

 Cretaceous deep sea faunas and offshoots of the Palaeozoic fauna." 

 Only 30 species were obtained, but four colonial genera were 

 represented ; of one, Lophohelia, Sir C. Wyville Thomson re- 

 marked 4 that it formed "stony copses which cover the bottom of 

 the sea for many miles." Of Dendrophyllia ramea, obtained in 

 the cruise of the yacht Noma, Saville Kent stated 5 that its 

 growths " were massive and weighty as any of the most solid 

 branching Madreporw of the Great Barrier Reef (of Australia)." 



L. F. de Pourtales obtained 6 six colonial genera of corals from 



1 On Chlorophyll from the Deep Sea. Proc. R. S. Edin., 1884—5. 



2 Sur la Penetration de la Lumiere du Jour dans les Eaux du Lac de Geneve. 

 Compt. Rend, xcrx., p. 783. 



3 Trans. Zool. Soc. Lond. viii., pt. v. 



4 The Deptlis of the Sea. 



5 Loc. cit., p. 72. 



6 Cat. Mm., Harvard Coll., 1871. 





