AN AITSTKALIAN SAUROPTERYGIAN ETHEBIDQE. 23 



There is a univalve in these hand specimens after the Euompha- 

 loid type, and in consequence of the direction in which the latter 

 have been cut, the sections are almost invariably across the 

 whorls. It is a small shell, the largest not measuring more than 

 three-eighths of an inch in diameter, biconcave, and the inner 

 whorls barely distinguishable. From the difference in outline 

 exhibited by the cross-section and the body whorls, I should 

 say two, if not three species are present. The next commonest 

 section is probably that of a Brachiopod, very geniculate in 

 outline, the sections passing from the umbo to the front margin 

 of either valve. One section in particular catches the eye from 

 the comparatively large process, projecting from underneath the 

 incurved umbo. This may be either a fulcrum supporting some 

 of the internal shelly plates of a Brachiopod, or a spoon-shaped 

 cartilage process of a Pelecypod, but I am inclined to the first 

 opinion. Several small circular bodies, hollow in the centre, about 

 three-eighths of an inch in diameter, and with median central 

 vacuities, are scattered at random through the rock. There is 

 no definite structure observable in these, but the size and general 

 appearance closely resemble that of the stem joints of many Crinoids. 



I am strongly of opinion that these highly opalised chocolate- 

 coloured quartzites are of Devonian age, being portions of travelled 

 blocks, in all probability coming from Mr. Jaquet's bed C. 



The whole of the specimens now under discussion, were submitted 

 to a careful examination by Dr. Thomas Cooksey, Mineralogist to 

 the Australian Museum, and myself. Dr. Cooksey is of opinion* 

 that in the chocolate quartzite the carbonate of lime of the fossils 

 has been in the first instance converted into crystalline calcite, 

 and the latter then replaced by secondary silicification in the 

 form of Precious Opal. The traces of the cleavage planes and 

 twinning of the calcite crystals are still preserved in the opal, 

 the former in a great measure serving to produce that play of 

 colour which gives to the opal its beauty and value. A few 

 instances of a similar process are certainly visible in the opalised 

 shells from the kaolin deposit, but in the majority of these there 

 appears to have been simply a secondary replacement by hydrous 

 silica of the ordinary carbonate of lime of the MoUuscan and other 

 tests. 



There is no trace amongst these fossils of the Beekite stage of 

 silicification. The occurence of this mineral in connection with 

 "Fossil Organic Remains" in N.S. "Wales is by no means an 

 uncommon one, and has already been noted by the Writer, f Such 

 occurrences, however, are confined to some of our Silurian and 

 Permo-Carboniferous fossils. 



* Eec. Aust. Mus., ii., 7, 1896, p. 111. 

 t Ibid, ii., 5, 1893, p. 74. 



