GENERAL DISCUSSION. 57 



in oyster shells by A. Liversidjje,"" and vanadium has been reported in the blood of an ascidian 

 by M. Henze,"' and in a holothurian by A. H. Phillips."- In short, a systematic search for 

 minor metallic constituents in marine invertebrates would probably show that they contain 

 many other elements. This subject, however, lies outside the scope of our investigation, and 

 these few citations are enough for present purposes. 



For the intensive study of coi-al reefs the analyses furnished by us together with those 

 cited from others are of great significance. The limestone immediately below the zone of 

 living forms owes its composition to all the organisms that flourished on the reef. Algie, corals, 

 alcyonarians, Foraminifera, and other forms of less importance contribute their remains to the 

 building of the limestone, which may vary in composition as the life upon it varies. Corals 

 may predominate in one place, algiB in another. Each reef must therefore be studied on its 

 individual merits if its chemical character is to be understood. Precipitated carbonates, 

 whether of bacterial origin or not, must also be taken into account, and their quantity may 

 be large. At Funafuti, where the Imiestone has been studied with imusual thoroughness, 

 the order of importance of the leading organisms is estimated by A. E. Finckh"' as follows: 

 1, Lithothamiiion;'''* 2, lialimeda; 3, Foraminifera: 4, the corals, including Heliopora and other 

 alcyonarians and the millepores. Here the corals are subordinate to the algip, and even the 

 Foraminifera outrank them. To call the Funafuti rock a coralline limestone would therefore 

 be somewhat misleading. 



At other localities the relative abundance of the marine organisms is different from that at 

 Funafuti. A careful analysis of samples from reefs at Murray Island, Australia, conducted by 

 T. Wayland Vaughan,"' gave the following results: "1,600 feet from shore, madreporarian 

 corals, 41.9 per cent; calcareous algae, 32.6 per cent; Foraminifera, 12.4 per cent; Mollusca, 10.2 

 per cent. At 200 feet from the shore the order is : Calcareous algae, 42.5 per cent; madreporarian 

 corals, 34.6 per cent: Mollusca, 34.6 per cent; Foraminifera, 4.1 per cent." Around the Tortugas, 

 according to L. R. Cary,"" the alcyonarian fauna is the most important contributor to the forma- 

 tion of reef limestones. He estimates the quantity of alcyonarian spicules at this locality to 

 average 5.28 tons to the acre; and at least one-fifth of this amount is added to the reefs annually. 

 In the Murray Island samples stutlied by Vaughan the alcyonarian remains were lacking. 



Chemical analj'sis, however, is not the only factor of importance in determining the com- 

 position of a marine limestone. The crystallme character of the shells and skeletons, whether 

 calcitic or aragonitic, must also be considered. For this purpose the well-known reaction 

 with cobalt nitrate, the "Meigen reaction," is commonly employed, especiall}' by W. Meigen 

 himself, who has studied a considerable number of organisms, both recent and fossil, and some 

 of his determinations "' relate to genera examined by us. For these, excluding fossil forms, 

 the data are as follows: 



Calcite. Aragonito. 



Lithothamnium, Alga. Ualimeila. -Mga. 



I.itliophyllum. Alga. Ciala.\aura. Alga. 



Polylrcma. Foraininifcr. Millopora. Hydromedusa. 



Coralliura. Alcyonarian. Histichopora. Hydroinedusa. 



Tubipora. Alcyonarian. llcliopora. Alcyonarian. 



Serpula. AnneUd. Spirula. Ccphalopod. 



Terebratula. Biachio|)od. Sepia. Cephalopod. 

 Argonauta. Cephalopod. 

 Balanus. Crustacean. 



» Liversidge, A., Jour. Chem. Soc., vol. 71, p. 298, 1897. 



«> Heiize, M.,Zeitschr.physiol.Chem., vol. 72, p.401, 1911, and vol. S6, p. 340, 1913. Henze also found copper in the liver o( cephalopods (idem, 

 vol.33, p. 417, 1901.) 



« Phillips, A. H., Am. Jour. Sci., 4th ser., vol. 46, p. 473, 1918. 



M The atoll of Funafuti, pp. 125-150, London, The Royal Society, 1904. 



«< The term Litfiothamnion as used in the Funafuti report is general and includes not only LUhothamniuvi but also LUhophylluiit, Ooniolitbon, 

 and perhaps other genera. See The atoll of Fiuiafnti, p. 3.32, London, The Royal Society, 19(M. 



" Vaughan, T. \V., Geol. Soc. America Bull., vol. 28, p. 942, 1917. 



« Gary, L. R., Carnegie Inst. Washington Pub. 213, 1918, p. 356. 



•' Meigen, W., Naturf. Gesell. Freiburg Ber., vol. 13, p. 13, 1903. 



