THE CHP:MICAL examination of the materials from FUNAFUTI. 375 



(a) Amoimt of Magnesium Car'honate secreted by Plants and Animals to form 



their Skeletons. 



That the calcareous skeletons of plants and animals contain minute proportions of 

 other salts, besides calcium carbonate, such as magnesium and iron carbonates, silica, 

 fluorides, phosphates, &c., is a fact that has long been recognised. Among these 

 adventitious substances the magnesium carbonate is usually the most abundant. The 

 earliest attempt to make accurate determinations of the proportion of magnesium 

 carbonate in the calcareous skeletons of plants and animals are those of Forchhammer, 

 whose pioneer researches upon the phenomena of dolomitisation are so well known. 



By the year 1849, Forchhammer had arrived at the conclusion, from numerous 

 analyses, that the amount of magnesium carbonate in fresh animal and vegetable 

 calcareous structures does not exceed 1 per cent, of their whole weight.* Benjamin 

 SiLLiMAN, JuNR., had already, in 1846, arrived at the conclusion, as we have seen 

 in- the preceding pages, that the proportion of magnesium carbonates contained in corals 

 is small, t 



That Forchhammer's general conclusions were correct has been proved by many 

 subsequent analyses by different chemists. Professor Liversidge in 1881 found in 

 a reef-coral from the New Hebrides only '17 per cent, of magnesium carbonate, but in 

 a coral limestone from Duke of York's Island he found 1 "808 per cent, of the magnesium 

 salt. I In 1894 Hogbom analysed several corals from the Bermudas, obtaining the 

 following results for the proportion of magnesium carbonate : — 



Porites sjd "62 



Millepora alcicornis . . . '41 and "97 



Oculina sp '36 



Coral from Java seas '16 



A number of univalves and bivalves from a coral reef yielded the same investigator 

 an average of only '16 of magnesium carbonate. § 



Three analyses of different portions of the shell of the giant-clam [Tridacna gigas, L.) 

 made in my laboratory, gave Dr. Skeats percentages of "36, "44, and '47 of magnesium 

 carbonate. 



Walther in 1885 obtained the following results from the analysis of forms belonging 

 to two genera of Polyzoa : — 1| 



Eschara foliacea . . . 1'2 of magnesium carbonate 

 Lepralia sp 2*2 ,, ,, 



* 'Oversigt over det Kongelige Danske Vidensk. Selskabs Forhaudl.,' 1849, pp. 83-96; Bidrag til 

 Dolomitensdannelshistorie ; Erdmann, ' Journ. Prak. Chem.,' vol. 49 (1850), pp. 52-64; 'Brit. Assoc. 

 Rep.,' 1849 (part 2), pp. 36-37. 



t 'Amer. Journ. Sci.,' 2nd series, vol. 1 (1846), p. 189, and 'United States Exploring Expedition' 

 (Zoophytes), 1846, p. 712. 



X ' Journ. Roy. Soc.,' New South Wales, vol. 14 (1881), pp. 159-162. 



§ ' Neues Jahrb. fiir Min., &c.,' 1894, I, pp. 268-9. 



II ' Zeitsch. d. Deutsch. Geol. Gesellsch.,' vol. 37, 1885, p. 338. 



