REPORT OR" THE DEEP-SEA DEPOSITS. 
285 
cent, of the whole deposit. The silica of these spicules is intimately associated with 
organic matter, the spicules being composed of alternate layers of opal or hydrated 
silica and organic substances.^ The percentage of water in the various analyses of 
Sponge spicules varies from 7 to 13 per cent.^ There is abundant evidence to show that 
these spicules are slowly dissolved in the sea- water after the death of the animal.® 
Fig. 32 . — PoUopogon amadou, Wyville Thomson (^). 
In addition to the Diatoms, Radiolarians, and Sponge spicules, there are large 
numbers of Foraminifera, Annelids, Crustacea, and Molluscs, which form their shells, 
tubes, and houses of Sponge spicules, Radiolarians, Diatoms, and other materials 
1 See Schulze, Report on the Hexactinellida, Zool. Chall. Exp., pt. liii. ; Ridley and Dendy, Report on the 
Monaxonida, Zool. Chall. Exp., pt. lix. ; Sollas, Report on the Tetractinellida, Zool. ChaU. Exp., pt. Ixiii. ; Thoulet, 
Gomptes Rendus, tom. xcviii. pp. 1000, 1001. 
^ Sollas, loc. cit:, pp, 47 et seq.; Thoulet, loc. cit. 
* Schulze, loc. cit., pp. 26, 27. 
