[Proc. Rot. Soo. Victoria, 34 (N.S.), Pr. IL, 1922.] 



Art. XVII. — On a Fossil Filanxentou8 Alga and Sponge- 

 Spicules forming Opal Nodules at Richmond River ^ N.S.W. 



By FREDERICK CHAPMAN, A.L.S., F.R.M.S. 



(With Two Text Figures.) 

 [Eead 10th November, 1921.] 



Source of Specimens. 



The samples of common opal from the diatomaceous deposits 

 of the Richmond River at Tintenbar, New South Wales, now 

 described, were handed oyer to the National Museum Collection 

 by Mr. R. H. Walcott, Curator of the Technological Museum, 

 Melbourne. They were received by Mr. Walcott from Mr. G. 

 N. Milne, of the Salvation Army, at Bayswater, on the 18th of 

 December, 1919. 



In response to Mr. Walcott's desire to know something of the 

 microscopic nature of these samples, I took thin slices from 

 two of the pieces, which gave different results; in the one case 

 a spicule-rock being revealed, originating from freshwater 

 sponges, and in the other the matted thalli of a confervoid fresh- 

 water weed, probably of the genus Cladophora, and now silicified. 



Literary Notes on tlie Deposit. 



Professor Liversidge, writing on the siliceous deposits from 

 the Richmond River, New South Wales,^ refers to this rock 

 as resembling ** the deposits thrown down by hot springs or 

 geysers." He records the presence of wood opal and remains 

 of ferns (Pteris) and seeds, one of the latter being named by 

 von Mueller, Liversidgea oxyspora,^ to which is also referred 

 a leaf fragment. 



J. Milne Curran, in writing on precious stones in New South 

 Wales,^ on p. 258 of the reference quoted, says, " I have more 

 than once received specimens of diatomite from the Richmond 

 River, which were in part converted into a true opal." 



1. Journ. and Proc. R. Soc. N.S. Wales, vol. X. (1876), 1877, pp. 237-240. 



2. Loc. cit., p. 239, plate. 



3. Journ. and Prtoc. R. Soc., N.S. Wales, vol. XXX (1896), 1897. 



