OPAL PSEUDOMOPvPHS from WHITE CLIFFS, 

 NEW SOUTH WALES. 



By C. Anderson, M.A., B.Sc, Mineralogist to tlie Australian 

 Museum, and H. Stanley Jrvons, M.A., B.Sc, late 

 Lecturer on Mineralogy and Petrology, University of Sydney. 



(Plates vi — vii., text fig. -1). 



The occurrence of Opal at White Cliffs as pseudomorphic crystals, 

 called locally "fossil pineapples" has been known for some time ; 

 they have been described by several observers, but no agreement 

 has yet been i-eached as to the species of the original mineral. 

 Recently se\eral good specimens have I'eached Sydney and were 

 examined by Professor T. W. E. David and the authors, the 

 conclusions arrived at being set forth in the present paper. 



Occnrreuce. — Before proceeding to the description of the speci- 

 mens themselves, their mode of occuirence, so far as known to us, 

 may be briefly alluded to. The White Cliffs Opal-field was first 

 geologically examined in detail by Mr. J. B. Jaquet, and it is cliiefiy 

 to his report^ that we must turn for our knowledge. The opal 

 is found in the Upper Cretaceous or " Desert Sand-stone" Series, 

 wliich at White Cliffs rests on Palyeozoic slates of probably 

 Silurian age. Overlying the Palaeozoic strata are (d) coarse grits 

 and sandstones, succeeded by (c) a thickness of fine white, kaolin- 

 like material of highly siliceous composition and containing large 

 waterworn boulders of quartzite with Devonian fossils. Con- 

 cretionary nodules, and moi'e rarely thin beds of gypsum occur in 

 these deposits. Above this are [h) conglomerates consisting of 

 small pebbles in a white siliceous mati'ix similar to c. It is in 

 the beds h and e that the opal occurs. It is often found replacing 

 various oi'ganic remains as Sauropterygian bones, Crinoid calices, 

 stems, and separate ossicles, Belenniite guards and bivalve and 

 univalve shells, as well as coniferous w'ood-^. 



1 Jaquet— Ann. Kept. Dept. Mines and A<?ric. N. S. Waler, 1892 



(1893), pp. 140—14.2. 

 - Ethpiidtre— Rec. Austr. Mup., iii., 2, 1897, p. 19; Mem. Geol. Surv. 

 N. S, Waifs, Pal. No. 11, 1902, p. 10; Rec' Austr. Mu.-.. v., 4, 1904, 

 pp. 248. 251 ; loc. cit., v., 5, 1904, pp. 306-316. 

 Pittman— Min. Kes. N. S. Wales, 1901, p. 405. 

 Tate— Trans. Roy. Soc. S. Austr., xxii.. 1898, p. 77. 



