SILURIAN AND DEVONIAN ROCKS. 1423) 
II. GEOLOGICAL FEATURES, 
The formations represented may be classified as follows: 
1. Recent Alluvium (of very limited extent) 
2. Tertiary (?) basalts, andesites, tuffs. 
3. Devonian—conglomerates, sandstones, quartzites, 
shales, etc. 
4, Silurian—limestones, claystones, tufis, rhyolites, etc. 
III. SrLURIAN (UPPER SILURIAN). 
Rocks of this geological age occur over a very large area 
in this part of N. 8S. Wales, but were only mapped so far 
as was necessary to determine their stratigraphical relation 
to the Devonian strata. They consist mainly of limestones, 
slates, tuffs, and contemporaneous rhyolite flows. 
A. The Limestones.—In the western portion of the area 
mapped, coralline limestones are abundant. A typical 
example (Bed A, see section) outcrops on portion 98, parish 
of Barton, close to the junction of Spring and Gap Creeks. 
(Plate 15.) This bed is about 20 feet thick and dips EH..10° 
S. at 38°. Traced to the north it disappears under a basalt 
flow, but reappears further on (portion 222), where it crosses 
the valley of Quarry Creek until it again disappears under 
basalt. The general strike of the bed is N. 20° W. A similar 
bed (Bed ©) outcrops further west (on portion 221) near 
the junction of Spring and Quarry Creeks. In both beds 
the corals are completely silicified and are beautifully 
preserved. 
The following fossils were obtained from these beds :— 
( Halysites lithostrotonoides 
Mucophyllum crateroides 
Endophyllum (?) 
| Favosites (Several species) 
| a australis 
| $5 pycnoblastoides 
| a Stissmilchii 
Actinozoa < e eratus 
| »  peristephesicus 
| 
