November, 1943 
The Queensland Naturalist 
77 
of great total thickness over both the schists and the meso- 
zoic strata, which have been intruded by sills and dikes. 
The surface on which they flowed was apparently not an 
even one. Between the flows there was often time for 
vegetation to grow on the basalt surface, now evidenced 
by charred wood and lignite. We do not know the former 
extent of these basaltic lavas, but we do know that it was 
very much greater than the present area covered for the 
simple reason that liquid lava, like water, flows in and 
floods the valleys or spreads over flat land, while the rock 
now occurs largely as mountain cappings with abrupt 
cliffs looking out over low country, from which) it and 
much underlying rock must have been removed by denuda- 
tion. Associated with these basaltic rocks are rhyolites 
and rhyolitic tuffs. The field relationship of these two 
very different types of rock are by no means clear, the 
more we see of them the more confused they seem (and we 
become). There is a lot of careful field observation requir- 
ed before we can hope for a solution. It is clear, from their 
present position, that these lavas, though of Cainozic age, 
are very far from recent, for an enormous amount of de- 
nudation has taken place since the streams first started to 
flow on their surface. Consider Tamborine, the Main 
Range at Cunningham’s Gap, Mt. Mistake, Mt. Edwards 
or the small area left at Mt. Glorious on the top of the 
D ’Aguilar Range, and what a long period of denudation 
they indicate. 
There is much scope for our geological observers to 
try and puzzle out the age of these basalts and their re- 
lationship to the basalt associated with the Tertiary de- 
posits near Brisbane and along the shores of Moreton Bay, 
and the part played by these rocks in the development of 
our present topography. 
May members of this Club find the solutions to the 
problems ! 
