Depth of core in feet. 



About 



15 



>> 



526 



)? 



598 



J) 



660 



?5 



690 



) J 



898 



)) 



1003 



95 



1108 



372 PROFESSOR J. W. JUDD. 



Percentage of calcium phosphate. 

 •136 

 •200 

 •124 

 •150 

 •168 

 •217 

 •195 

 •288 



By the method of analysis adopted, the presence of phosphates would be at once 

 indicated, and if they had occurred in marked quantity in any sample taken for 

 analysis, the circumstance would have been at once detected. It M^as found, on the 

 contrary, however, that the amount of this constituent was always minute, and, in 

 some cases, nearly inappreciable, in the case of every sample taken. In the analyses 

 of the raised coral-reefs from the Indian and Pacific Oceans, which Dr. Skeats made 

 on the materials supplied by Sir John Mukray, Professor Alexander Agassiz, and 

 Profess(jr T. Edc4EW0RTH David, calcium pliosphate was found to exist generally as 

 a mere trace. The highest })ro])ortions fcmnd were ^29 in a rock from Mango in the 

 Fijis, ^064 in a rock from Ngihingillah in the same group, ^22 in a rock from Niue or 

 Savage Island, and "15 from rocks at Cliristmas Island. 



From these results, compared with those quoted from Harrison and other authors, 

 it may be safely concluded that the rocks of Funafuti agree with most coial-reef 

 formed limestones in containing only very minute traces of calcium phosphates — rarely 

 if ever exceeding 0^2 per cent. 



As is so well known from the exanq^les at Christmas Island and the Clipperton 

 Atoll, described by Mr. Teall,* coral-island rocks which become the haunts of 

 sea-birds may be covered with extensive deposits of guano, the water percolating 

 through which may convert the underlying rocks into materials rich in phosphates, 

 ^liich are sometimes of great economical value. 



A rock obtained l)y Pi-ofessor Sollas from behind the Mangrove Swamp near 

 Fongafale in the main island of the atoll was of a dark brown tint, and was found by 

 liim to be rich in phosphoric acid. The soil of theTaro plantation near this point had 

 been collected by Mr. Hedley, and on analysis by Dr. CooKSEYf was found to contain 

 6 per cent, of phosphoric acid. 



Analyses of two samples of rock brought from this locality by Professor Sollas 

 yielded respectively 21 "64 and 29'07 per cent, of calcium phosphate. In the islet of 

 Avalau, lying noi'th of the main island of Funafuti, two other specimens of a brown 

 rock forwarded by Professor Sollas, yielded Dr. Skeats on analysis 14^40 and 



* ' Quart. Journ. Geol. Soc.,' vol. 54 (1898), pp. 230-232. 

 t Memoir 111., Au.stral. Museum, Sydney, p. 7G. 



