THE AUSTRALIAN NATURALIST. 61 
The life of the period was illustrated by lantern views 
of characteristic fossils—both animal and plant, the ab- 
sence of the higher types of both kingdoms of nature at- 
testing the stage of physical evolution reached. 
The next great division in the Section—the Trias—was 
described as beginning immediately above the top coal- 
seam, and consisting of three great divisions in ascending 
order—the Narrabeen beds, the Hawkesbury sandstone, 
and the Wianamatta beds. 
Though no stratigraphic break occurs between the 
Upper Coal Measures and the Trias, the regular sequence 
being maintained, nevertheless, paleontology indicates 
(with one solitary exception that proves the rule) a mark- 
ed palentological unconformity; the abundant and char- 
acteristic Glossopteris flora of the coal measures abruptly 
giving place to sparsely represented, and mostly macer- 
ated, plants of a later age, and with them Mesozoic fish 
and labyrinthodont remains. 
The Hawkesbury series, which form such stupendous 
cliffs on the seaboard and in mountain gorges, were cited 
as an instance of estuarine deposition in a slowly subsiding 
basin—one continually being filled, yet never full—the 
rate of subsidence and filling being about equal, as wit- 
ness the enormous thickness of sedimentation bearing 
throughout evidences of shallow deposition—in wave- 
marks, current-bedding, ,sand-cracks, and rain-prints. 
The well-known ‘‘Chocolate Shales’’ were pointed out 
as the dividing line between Narrabeen and Hawkesbury. 
These shales consist of finely triturated volcanic dust from 
volcanic outbursts, contemporaneous with the deposition. 
The Wianamatta Shales, which mark the close of the 
Triassic period, consist mainly of fine still-water sedimen- 
tation in lakes, or eroded hollows, of the Hawkesbury 
sandstone; surface plasticity, and absence of coarse sand 
render these shales eminently suitable for brick and _pot- 
tery purposes, for which they are largely utilised in the 
vicinity of the metropolis. ~ 
The characteristic fossils of the Trias were shown on 
the screen. All the animal types belong to fresh or 
brackish water conditions, with the doubtful exception of 
a reappearance of a detached silurian form (7'remanotus 
Maidenw) at Cockatoo Island, and the undoubted occur- 
rence of Foraminifera at Kurrajong, which appears to 
prove subsidence, and encroachment of the sea, about the 
close of the Wianamatta. 
