294 
Geology of Sydney. 
a mountain tract from its latest appearance from 
beneath the sea. Looked at in this way, the Moun- 
tains are, comparatively speaking, modern, for the 
area occupied by them was depressed below the sea 
in Devonian, Permo-Carboniferous and Triassic times. 
There is no evidence that the Blue Mountains 
were under water since Triassic times, and we there- 
fore conclude that the range was upheaved sub- 
sequent to the Triassic period. 
During the deposition of the Devonian sediments 
we laid a comparatively shallow sea, with dry land 
covered with a vegetation. About this period, molten 
or semi-plastic granites were slowly eating their way 
upward, and absorbing at the same time much of the 
overlying sediments. 
In Permo-Carboniferous days the area we are 
dealing with was also submerged, but under condi- 
tions alternately fresh-water and marine. The 
physical features were not unlike some parts of the 
earth’s surface to-day. The whole area was under- 
going prolonged depression. Volcanic phenomena 
were much in evidence, but none of the present 
mountain peaks stood above the general level. 
During the succeeding Trias or Trias- Jura period, 
no elevatory movements took place. Slow subsidence 
was still in progress, but a great change was impend- 
ing, and the first symptoms of mountain building 
were about to manifest themselves. Through the 
long preceding periods, the materials were accumu- 
lating that go to make the Coal Measures, Sandstones, 
