THE CHEMICAL EXAMINATION OF THE ^fATERTALS FROM FUNAFUTI, 

 Some of the numbers thus obtained were as follows : — 



3()'J 



Number of 

 core. 



Depth in feet. 



Weight of rock 

 dissolved. 



Percentage 

 of insoluble residue. 



6 

 192 

 364-5 



72a 

 384a 

 652a 



10 



260 



670-698 



763-771 



922-936 



1075-1087 



91-50 grammes 



52-07 



70-07 

 167-18 

 100-4 

 122-4 



•003 

 •083 

 •006 

 •001 

 •013 

 -004- 



In the case of the largest of these residues, that from 260 feet, an attempt was 

 made to determine its composition. Only '04 gramme was available, but on fusion 

 with carbonates and ignition this yielded 12 7 5 per cent, of silica, the dissolved 

 portion consisting principally of ferric oxide and alumina. 



Very similar results have been obtained by Mr. Stanley Gardiner in examining 

 a series of coral-rocks and " coral-sands" from the Maldive atolls.* In these, analysis 

 showed that the quantity of silica present varied from "0013 to '076, omitting the 

 cases in which argillaceous matter might have been present. The average of nine 

 examples from Minikoi gave only '046 per cent, of silica ; a specimen from Hulule 

 gave '024 per cent, of silica ; while the average of four specimens from Suvadiva gave 

 only '003 per cent, of silica. The bases found to be present by Mr. Stanley 

 Gardiner were calcium, magnesium, aluminium, and iron. 



The series of specimens from Christmas Island and from the raised reefs of the 

 Pacific, for which I am indebted to Sir John Murray and Professor A. Agassiz 

 respectively, have afforded to Dr. Skeats the means of determining the amount of 

 insoluble inorganic matter from widely separated coral reefs all over the globe. He 

 found in all cases that " insoluble residue is present in exceedingly small quantities," 

 except where the limestones are associated with volcanic rocks, t 



This minute proportion of insoluble residue in the Funafuti rocks appears at 

 first sight somewhat difficult of explanation. Dr. Hinde and Mr. Kirkpatrick show 

 that traces of siliceous sponges are present both among the organisms collected on 

 the reef and also in the rocks of the reef brought up as cores from the borings. 

 Indeed, as Dr. Hinde has pointed out, the borings of Cliona are very frequent. It 

 would appear, therefore, that the colloid silica of sponge spicules and of radiolarians, 

 diatomacese, &c., must, under the conditions that are present in the reef, pass again 

 into solution before the silica is converted into the crystalline and insoluble form. 



There is another source of insoluble matter which must not be overlooked. In the 



* ' The Fauna and Geography of the Maldive and Laccadive Archipelagoes,' vol. 1, Part 3, 

 pp. 322-323. 



t 'Bull. Mus. Comp. Zool. Harvard College,' vol. 42 (1903), p. 103. 



3 B 



