SILURIAN AND DEVONIAN ROCKS. 137 
about 54°, whereas the topmost bed of the Silurian strata 
(the Red Tuffs) dips in the same direction at an angle of 
about 65°. This would seem to indicate an unconformity 
between the two series. A reference to the accompanying 
section, however, will show that the Devonian beds, from 
the axis of the synclinal fold, where they are for a short 
distance horizontal, show a constantly increasing dip as 
the junction referred to is approached, while the dip of the 
Silurian strata increases beyond the junction until they 
become nearly vertical. Owing to the way in which the 
strata at the junction have weathered, and the absence 
in them of well defined bedding planes, the determination 
of the dip with any degree of accuracy is almost impossible. 
In the Oaky Creek section, further north, the Devonian 
conglomerates appear to rest conformably upon the Silurian 
tufis, but here again the outcrops are not very satisfactory. 
The mere presence, at the base of the Devonian strata, of 
massive beds of conglomerate, indicates a pronounced uplift 
in the vicinity initiating a new cycle of erosion. The 
pebbles found in the conglomerates are all such as might 
have been derived from the Silurian strata. These facts 
point toa deforming movement having effected the Silurian 
strata prior to the deposition of the Devonian sediments 
with the resulting production of an unconformity. 
Comparison with other New South Wales Devonian strata. 
—The best known Devonian strata in New South Wales 
are those occurring at Mount Lambie near Rydal; these 
consist mainly of shales, sandstone, and quartzites, and 
contain numerous fossils such as Spirifer disjuncta, Rhyn- 
conella plewrodon, Lingula gregaria, and Lepidodendron 
australe. These beds are generally referred to as being of 
Upper Devonian age. At Back Creek near Braidwood, 
New South Wales,” by Prof. T. W. E. David and E. F. Pittman. Rep. 
Austr. Assoc. Adv. Sci., Adelaide, Vol. v., (1893) pp. 397 - 404. 
