AN AUSTRALIAN SAUROPTERYGIAN — ETHERIDGE. 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 silieification 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 Molluscan and other 
tests. 
There is no trace amongst these fossils of the Beekite stage of 
silieification. 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. 
* Rec. Aust. Mus., ii., 7, 1896, p. 111. 
f Ibid , ii., 5, 1893, p. 74. 
