NEWTON: OPALIZED SHELLS OF NEW SOUTH WALES. 219 



The evidence of these fossils, consisting of terrestrial, fresliwater, 

 and marine organisms, clearly proves the estuarine origin of the opal 

 deposits of New South "Wales, and their association with the opalized 

 coniferous wood {Araucarioxijloii sp. of Giirich) further accentuates 

 this view. Although the fauna, so far as we know it, is quite 

 endemic, yet it is of interest to point out that a somewhat similar 

 assemblage of forms characterizes some of the estuarine deposits 

 occurring in the Cretaceous strata (f N'orth America. For instance, 

 the Judith River group of rocks in the Wyoming region of the 

 United States, which are of the latest Cretaceous age, have yielded 

 both Corbicula and Dinosaurian remains in association. Then, again, 

 there are the Belly' River deposits of Canada (Alberta), of somewhat 

 similar age, which contain Plesiosaurian {Cimoliosmiriis) and Dino- 

 saurian bones, as well as Unioniform shells, Corbicula, Viviparus, 

 etc., and those of marine habit like Pteria, Jfi/tihis, Ostrea, etc. 

 (Whiteaves, Geol. JS'at. Hist. Surv. Canada, vol. i, p. 55, 1885). 

 The Belly River and Judith River beds are recognized as belonging 

 to the Montana epoch (see Chamberlin & Salisbury, Geology, vol. iii, 

 p. 152, 1906), which represents very high Cretaceous, or probably 

 what may be the equivalent of the Danian of Europe. It is, 

 therefore, possible that the opalized deposits of Australia were laid 

 down at nearly the end of Cretaceous times. It often happens that 

 these mineralized shells, before they reach the palaeontologist, have 

 been polislied by the lapidary to intensify their opalescent characters, 

 an operation which of course is very much to the detriment of the 

 finer structures of the fossils, although among the specimens to be 

 noticed are those which have escaped such treatment and in which 

 the details of sculpture have been preserved. 



I wish to record my indebtedness to Mr. Spencer for giving me 

 facilities to examine Australian opalized shells in the Mineral 

 Department of the British Museum, to Messrs. E. A. Smith and 

 G. C. Crick for information on certain of the MoUusca, as also to 

 Drs. A. S. Woodward and C. W. Andrews for suggestions in connexion 

 with the vertebrates found in the same deposits. 



Bibliography. 

 The opal deposits of White Cliffs were first noticed by Mr. W. 

 Anderson'' in 1892, who described them as very siliceous, horizontally 

 bedded sandstones of Upper Cretaceous age, and the probable 

 equivalent of the Desert Sandstone of Queensland ; in close proximity 

 were vertical Silurian slates and horizontally bedded Devonian 

 conglomerates and sandstones. Reference was also made to the 

 original structures of the Mollusca, wood, Encrinites, etc., found in the 

 beds being replaced by opaline matter. Mr. Anderson regarded opal 

 as a secondary product of igneous rocks, sandstones, limestones, etc., 

 which is usually the result of deposition from opal-silica solutions 

 percolating through the rocks. 



' According to the latest information from Canada, this river is now to be 

 known as the Lethbridge Eiver. - 



^ " Notes on the Occurrence of Opal in New South Wales " : Eec. Geol. Surv. 

 N.S.W., vol. iii, pt. i, pp. 29-32, 1892. 



