368 PROFESSOR J. W. JUDD. 



home by Mr. Finckh, to illustrate the method and growth of corals. We have 

 examples of AsU'CBoj^ora and other forms, in which a mass of dead and much decayed 

 coral is being enveloped in a fresh layer formed by the calices of living polyps. 



Benjamin Silliman, June., estimated the proportion of organic matters present 

 in various genera of corals as varying from 2-8 per cent.* 



S. P. Sharples, analysing a series of specimens dredged by Count Pourtales 

 off Florida and Cuba, found the limits of the proportions of organic matter and 

 water, taken together, to lie between 1 and 4 per cent.t 



The analyses made of corals and coral-reef rock by Professor Liversidge| indicate 

 the presence of an even smaller proportion of organic matter in such materials, for he 

 found less than I per cent, of water and organic matter, taken together, in a reef-coral 

 from the New Hebrides. Later analyses by different chemists seem to indicate that 

 the quantity of organic matter retained in dead coral is generally very small 

 indeed. 



The analyses of the Funafuti cores indicate that in the surface rock the quantity of 

 organic matter is small, seldom, if ever, exceeding 1 per cent. ; that at a depth of 

 50 feet it is so minute as to be safely negligible, while at depths below 100 feet 

 the quantity of organic matter is quite inappreciable. 



5. Proportion of Insoluble (Inorganic) Matter in Coral-Reef Rocks. 



The study of this subject in the case of the materials from Funafuti, has led to 

 some very interesting results, which have an important bearing on certain geological 

 questions. 



When, after being prepared in the manner described in the foregoing pages, the 

 samples from Funafuti were dissolved in acid, it was found that the quantity of 

 insoluble residue was, in all cases, almost inappreciable. As every specimen had to 

 be dissolved for analysis, it was obvious that there could be no room for error on this 

 point. In order, however, to remove any possibility of doubt, large quantities of 

 material were from time to time submitted to solution, but always with the same 

 result, a very minute quantity of insoluble matter being left behind. 



As a final check to these results I requested Dr. Skeats to dissolve very 

 considerable quantities of the rock taken at different depths from the bore-hole, and 

 after submitting them to slow solution in very dilute acid, so as to avoid risk of 

 decomposition of basic or hydrous silicates, to weigh the residue (always a very 

 minute one) in each case. These tests were repeated from materials taken at 

 intervals all down the bore-hole, till there could be no doubt as to the result. 



* ' Amer. Journ. Sci.,' 2nd series, vol. 1 (1846), p. 189. See also 'Report of the United States 

 Exploring Expedition (Zoophytes),' 1846, p. 712. 



t ' Amer. Journ. Sci.,' 3rd series, vol. 1 (1871), p. 168. 



X ' Journ. Royal Society of New South Wales,' vol. 14 (1881), pp. 159-162. 



