November, 1943 
The Queensland Naturalist 
73 
They total an immense thickness of sediments and 
lavas, estimated by him at 75,000 feet, which were subse- 
quently crumpled, twisted and tilted, and altered to vary- 
ing degrees by heat, compression and shearing so that now 
they mostly lie at very steep angles with a prevailing 
N.N.W.-S.S.E. strike. What is their geological age or 
ages? Geologists have sought vainly for fossils and specu- 
lated almost as vainly. A few years ago Mr. L. C. Ball 
found some marine fossils of carboniferous age at North- 
brook in rocks which until then were accepted as part of 
the schist series, but further examination has led some to 
the opinion that they belong to a more recent series. 
Members of this Club may perhaps be lucky enough 
to find a fossil-bearing locality in the so-called schists or 
succeed in puzzling out the structure of the complex of 
varied rocks, and their relationship to the carboniferous 
strata at Northbrook. 
. The steep dips and almost uniform strike of these 
ancient strata indicate that after their deposition there 
must have been a period of mountain forming to which 
nothing comparable has since happened in this part of 
Queensland. The upturned and elevated rocks thus ex- 
posed to denudation became worn down to a surface which 
seems to have been somewhat similar to the surface of the 
same rocks at the present time. On this hilly land-surface, 
in Triassic times were laid down the extensive fresh-water 
formation of the Ipswich coal-measures and Bundamba 
sandstones and Walloon Coal-measures in continuous 
sequence. 
In the Esk district there are Triassic strata under the 
Ipswich. In the neighbourhood of Brisbane the very be- 
ginning of the deposition of the Ipswich coal measures, 
and cessation of denudation of the then existing land was 
ushered in by an eruption of volcanic ash, the land being 
covered and thus preserved by what is now known as the 
Brisbane Tuff. 
Preservation of vegetated swamps under subsequent 
sandstones or shales is, of course, a feature of all coal- 
measures, and the preservation of the vegetated surface 
under and between lava flows is also common, as for in- 
stance at Tamborine Mountain, but it must be surely a 
great rarity for a land-surface, an ordinary hilly land- 
surface to be preserved by being covered with a 
