78 
The Queensland Naturalist. August, 1935. 
NOTES MADE ON EASTER EXCURSION, QUEENS- 
LAND NATURALIST CLUB, 1935. 
Geology of the Upper Nerang Valley. 
By E. 0. Marks, M.D., B.E. 
As has been the experience on most of our excur- 
sions, the three or four days proved insufficient to attain 
a clear understanding of the local geological features, 
though as usual, providing ample material to show the 
structural problems awaiting solution and contributing 
something towards that end. There is ample fieldwork at 
Numinbah to occupy many Easter excursions. 
It often happens in geological work that an area 
which, on slight acquaintance, seems capable of a simple 
and satisfactory interpretation is found, on closer ac- 
quaintance, to be much more complicated than was prev- 
iously thought. This is the case with the Numinbah region, 
and the excursion has left us in a greater fog than when 
we started, except that we are clearer as to what we do 
not know and what we need to find out. 
The geology of the Numinbah or Upper Nerang 
Valley, is largely a continuation of that investigated on 
our excursions to Canungra, and reported in the ‘ ‘ Queens- 
land Naturalist,” of July, 1928. For those not familiar 
with the essential features it may be well briefly to re- 
count them. 
The oldest rocks in this corner of Queensland belong 
to the extensive series known as the Brisbane Schists. They 
are a group of very ancient sediments, whose age or ages 
is not definitely known, though part is probably Lower 
Carboniferous, as indicated by fossils discovered recently 
by Mr. L. C. Ball, at Northbrook, in the Brisbane Valley. 
The sediments have suffered varying degrees of folding 
and metamorphism. In the area we are dealing with they 
are of the class known as greywacke, which is an altered and 
compacted sediment, coarse or fine in grain, consisting 
of rock debris rather than quartz sand, as is the case with 
ordinary sandstones and its altered form quartzite. 
After these ancient sediments had been folded and 
subjected to metamorphism, they were exposed to denuda- 
tion. On an uneven surface, carved out of them by denud- 
ation, the extensive fresh water deposits of mesozoic time 
were laid down. Near Brisbane the Triassic “ Ipswich” 
coal measures, mainly shales and sandstones, were immedi- 
ately preceded by a varying thickness of trachytic volcanic 
ash, under which is a little shaley material, with silicified 
tree trunks, representing probably the old land surface, 
soil and drift, buried by the; volcanic ash. This “ Brisbane 
