168 F, Chapman: 



The most important contribution on the diatom deposit of the 

 Richmond River is that by Messrs. G. W. Card and W. S. Dun.* 

 A copious quotation bearing on the present work is as follows : — 



" Wyrallah. — The deposits on the Richmond River appear to- 

 be typically developed at Wyrallah, nine miles from Lismore. 

 Here there seems to be a number of scattered deposits on either 

 side of the Richmond River. They are surrounded and over- 

 lain by scoriaceous basalt, and occur in depressions in the same 

 rock. Probably large areas of the diatomaceous earth have been, 

 washed away. It has been stated at various times that consider- 

 able thicknesses of the earth exist in private lands, but this 

 requires confirmation. The physical character of the diato-- 

 maceous earth from these deposits is peculiar. It is hard and 

 stony, requiring considerable pressure to crush it, and it is of a 

 dirty white colour. The percentage of silica is high — over 90 

 per cent., and the lower portion of the deposit merges into a 

 band of yellowish common opal, about a foot thick. Pieces of 

 the opaline rock are marginally earthy, due probably to the re- 

 moval by solution of the secondary silica, as in the case of chalk 

 flints. The rock is isotropic, and marked with parallel bands, 

 coloured by splashes of yellow and brown. ^ With a high magni-^ 

 fying power the base is seen to be made up of hazy wisps and 

 shreds, and numerous indistinct fragments of Melpsira. This- 

 has been remarked on by the Rev. J. Milne Curran."® 



Some interesting " Notes on a Plant-bearing Common Black 

 Opal from Tweed Heads, N.S.W."^ have been published by Prof.. 

 E. W. Skeats. The opal occurs associated with basalt fliows^ 

 and, although the age of the basalt is left open by Prof. Skeats,. 

 yet the occurrence of the freshwater algae in the opal at any 

 rate points to similar conditions of deposition that wfe infer from 

 the opal of the Richmond River now under discussion. It will 

 be here appropriate to quote part of the remarks of Prof. Ewart 

 upon the structures found in the opal, recorded on p. 21 of Prof. 

 Skeats* paper: "Some of the structures appeared to represent 

 sections of fresh-water algae, others of various plants, including 

 the spore of a fungus, a transverse section of a leaf, and, possibly, 

 a section of a small petiole." 



4. Rec. Geol. Surv. N.S. Wales, vol. V., pt. 3, 1897, pp. 143 and 144. 



5. This description applies to the present specimens. 



6. " This " refers to the opal, and not to its contents^ as a reference to- 

 Mr. Ciurran'a paper will show. 



7. Proc. Roy. Soc. Queensland, vol. XXVI., 1914, pp. 18-22, pla. I. and II- 



