August, 1926 
93 
The Queensland Naiuralist. 
Tlie Brisbane tub* is a rattier soft roek, which does 
not stand attrition at all well, and would soon be ‘rroiuid 
down to powder in a stream. It is unlikely to have been 
carried 14 miles in a coarse <rrave4 hut cannot be quite 
excluded on that account. If the ])ebble is a frap:ment 
of Brisbane tuff, tliis would show definitely that the 
sandstone is of Tertiary ajje, not Bundamba. for the Bun- 
daniha sandstone follows in comfortable and overlapping 
sequence on the Ij)swich measures, under Avhieh the tuff 
lay buried. N'o fraoanent of the tutf could have lieen 
available until earth movements and denudation had 
exposed it, lon^ after Bundamba times. 
Xow, the other trachytic eruptions, Flinders Peak, 
Glass House Mountains, etc., have usually been re»’ard- 
ed, though without absolute proof, as of Tertiary a^e. 
They are 'almost certainly later than tlie Bundanba 
sandstone, and it is more than likely that the Point 
Lookout eruption belongs to the same idiase of 
volcanieity. 
If our Dunwicli ])ebble came^ as seems likely, from 
the Point Lookout lava, it means that either the Dunwich 
sandstone is of a later ])eriod in the Tertiary or else 
that if the sandstone is Bundamba, the Point Lookout 
eruption occurred previous to that. 
As there is no evidence that the sandstone is part 
of the Bundamba seines, Ave are justitied in sayino- that 
the probability is stron^dy in faA'our of it being* of 
Tertiary age, and this view is strengthened by the 
recent investigation of Messrs. C, (\ Morton and Owen 
Jones, Avho both regai’d tiie loose sandstone at Humpy- 
bong as of Tertiary age. 
We must, hov'ever, clearly bear in mind that the 
age of the Dunwich rock is not yet proA^ed, though the 
pebble has gone a long Avay to solve the problem. 
If, as seems ]U‘obable noAv, the Diunvich sandstone, 
as Avell as that of Pee] Island and (-^oochi-mudlo is 
that of Tertiary age, this giA’es a large extension to the 
already knoAAUi areas of post-mesozoic deposits near 
Brisbane. It also opens up the question of the distribu- 
tion of land and Avater in Tertiary time, for there is 
nothing now but sand dunes betAveen the DunAvieh sand- 
stone and the ocean beach. 
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