AN AUSTRALIAN SAUllOPTERYQIAN — ETHERIDQE. 
21 
specimens hardly any structure at all is to be observed, beyond 
the outward form of stem or branch, as the case may be. Not 
infrequently radial cracks are filled with Precious Opal, when the 
play of colour is very line. 
The Animal Remains occur under the following conditions : — 
1. As external or internal casts in kaolin, without opalization 
of any kind. 
2. Entirely converted into hydrous silica or Common Opal, 
white and opaque, but occasionally with traces of the coloured 
variety scattered through. 
3. Wholly or partially converted into translucent-glassy to 
vitreous semi-opaque Precious Opal, displaying a line range of 
colour. 
The colours visible by reflected light are principally blue, red, 
green, and yellow, with their various shades and combinations, 
hot the least pleasing being an ever-varying degree of red and 
blue-tinted purple. 
When the fossils are in the form of kaolin casts, specific 
identification, with a very few exceptions, is almost unattainable. 
Those in which opalisation, however, has taken place, are always 
determinable, more or less, and the substitution of the original 
carbonate of lime has been very thoroughly carried out. Frag- 
ments of these opalised remains, chiefly shells, are freely scattered 
throughout some hand-specimens til* the opaline kaolinised con- 
glomerate, from the bed 11 of Mr, Jaquet’s section.* The kaolin 
casts are either white or tinged with iron oxide, arising from the 
highly ferruginous clays that Mr. Jaquetsays the kaolin passes into. 
The opalised fossils comprise Crinoid remains, the shells of 
Pelecypoda and Gasteropoda, portions of Heleranite guards, and 
Sauropterygian hones. The preservation of some of these fossils 
is excellent, although all are not alike in this respect, and the extent 
to which the opalisation has at times been carried is remarkable. 
In some Pelecypoda, the external growth laminin, and inter- 
mediate sculpturo stria* are fully preserved, whilst the shell 
substance is completely changed, and by transmitted light the 
valves of many are almost transparent. On the fractured edges 
of one of these bivalves the glassy opal is quite translucent by 
reflected light. When such valves are met with in apposition, 
the interiors are often found to be filled with soft kaolin, and 
no better examples of the complete change that lias taken place 
can be examined. 
The replacement of the fibrous calcite of the Belemnite guard, 
when viewed in cross-section, presents a far less translucent, and 
*Ann. Rep. Dept. Mines and Agrie. 1892 [1893], p. 141. 
