GEOLOGY OF THE COOMA DISTRICT, N.S.W. ONS 
stated about the question, and of course it is very doubtful 
whether the matter will even be settled by future inves- 
tigation. 
V. Geological History up to Tertiary Times. 
We can to some extent trace the sequence of the events 
which have formed the geological history of the region. In 
Ordovician times the whole extent of the country was a 
great sea, in which sandy and muddy sediments were 
deposited to a considerable thickness: later, in Silurian 
times, marine conditions still obtained over part of the 
area at any rate, with deposition of limestones, shales, 
sandstones and grits. These last would appear to mark a 
change to shallower water conditions, possibly indicating 
a positive movement of the earth’s crust. Uplift of the 
area followed, with great earth movements and intense 
folding along a nearly meridional axis. What was in Silurian 
times a sea now became dry land, and has not since been 
submerged. 
Subsequently to this uplift, during Devonian or Car- 
boniferous times, intrusions of porphyry, granite and syenite 
took place. Very extensive denudation and base-levelling 
must have occurred, and was probably repeated as a result 
of successive uplifts, so that before the outpouring of the 
Tertiary lavas the physiography of the country had reached 
a state of considerable maturity. The granite and syenite 
had been laid bare by erosion, and the ancient corrugations 
of the Ordovician and Silurian rocks had been smoothed 
out by denudation. 
VI. Physiography. 
The geological history from the Tertiary till now is really 
the history of the present topography, and is best to be 
learnt by considering and studying the surface of the 
country as it now exists. 
