10 
Classification of Rocks 
any reason for supposing that the whole mass of sand¬ 
stones, shales, limestones, and coals does not form one 
continued and connected series of rocks. The few and 
detached observations I was able to make did not give 
me a decided clue to their order of arrangement; but I 
am inclined to suspect the limestones to be near the top, 
and the coals near the bottom of the series. The fossil 
shells belonged to the genera Spirifer, Producta, Lcpta ?- 
na, Pecten, Avicula, Plcurorynchus, and imperfect casts 
of several bivalve shells, which may be Cypricardia, Cucul- 
Icea, Sec. The corals chiefly belong to the genus Fcnestclla. 
One or two species of shells are very closely allied to 
European and British species; among these a Producta, 
that appears to be P. scabricula spirifera, like Sp. glabra 
or oblata, and a long-winged one like those of Devon¬ 
shire. The Fenestellat are very nearly the same as those 
figured in Phillips’ Palmozoic fossils of Devon and Oorn- 
wall. The whole assemblage of organic remains put me 
very much in mind of the Devonian fossils. Again, many 
of the plants from the coal shales are very like those of 
the carboniferous system of England, while some I had 
never seen before : but, in the absence of all works of 
reference, mere general recollections of forms must neces¬ 
sarily be very vague. There are, however, certainly 
species of the genera Calamites, Neuropteris, Sphcno- 
pteris, Cyclopteris, and others. The thickness of the whole 
formation must be very great. Grass Tree Hill, near Ho¬ 
bart Town, shows a mass of sandstones, with an occasional 
bed of shale, upwards of 1000 feet thick, lying nearly 
horizontally. 
The same formation is found around Sydney, extending 
from the Blue Mountains to the coast, and, as my friend 
the Reverend W. B. Clarke, of Paramatta, informs me, 
occupying all the country from the Hunter to the Illa- 
warra district at least. Sir T. Mitchell was kind enough 
