-92 
August, 1926 
riie Queensland Naturalist. 
of tracliTtu* lava, a fact not previously recorded. This 
year we were able to exauiine the sandstone, well known 
to occur at Dnnwieti. 
This is a clayey, ferrugineous, coarse'jjrained massive 
sandstone. Such bedding: as it has shows it to be nearly 
horizontal. Similar sandstone occurs also at Peel and 
Coochimiidlo Islands. This has usually been rejrarded 
as ]>art of the very extensive Bundaiuba ^lezozoie 
samlstone series, wliich immediately overlies the Ipswich 
coal measures, typical Ipswich measures occurring on 
the mainland shore at Wynnum and Manly, Unfortu- 
nately, the coarse-grained and loosely cemented sand- 
stone at Dumvich is not a likely matrix for tlie pre- 
servation of fossils by means of which its age could be 
determined. 
AVhen examining the water-worn (luartz ])ebbles of 
whicli the coarse-grained portions are composed, w(‘ were 
fortnnate in finding one pebble of weathered trachyte 
or Trachytic 'tuff, which is of almost as great interest as a 
fossil wonl<l liave been. 
Jn its deeomposed ground mass of felspathic material 
are embedded numerons phenocrysts of quartz with 
sharp erystalline outlines, often i)artly corroded by the 
magma or fragmentary, but none showing any rounding 
by attrition. The ground mass sliows a tendency to a 
flow structure, suggesting the fragment to be a lava 
ratlier than a tntf. 
In com]>arison, the trachytic Brisbane tuff, so 
familiar to us all, shows very similar quartz-grains in a 
felspathic gronml ]nass, the (piartz-grains being almost 
as numerous, hut with a greater tendeney to he frag- 
mental. and sometimes with a struetui'e suggestive of 
a flow. Some of the rhyolite at Point Lookout also 
shows very similar (piartz phenocr\-sts, many a])parently 
fragmentary, corroded by the magma as in the pebble, 
though not so numerous, and Avitli a marred flow struc- 
tni'(\ 
Now. the Brisbane tuff lies at the very base of the 
Ipswich measures, and tlie nearest known outcrops 
occur at (’astra and Tingalpa, some 14 miles from 
Dnnwieh in a wt'sterly direction. The nearest known 
traehytie lava is Point Lookout, 10 miles to the north- 
east. Tlie next nearest being some 40 miles distant. 
As a source of origin for this pebble, we must look 
■either to the Brisbane tuif or Point Lookout. 
