104 
The Queensland Naturalist 
August. 193S 
one point be traced continuously under the sand dunes 
to the peaty material in the swamps behind the dunes. 
In type the brownish black sandstone is similar 
to that at Tweed Heads, and at so many 
places along the coast of South Eastern Queens- 
land. It may have preserved in it well developed 
roots of trees which once grew in it, and people 
speak of these as being remnants of a fossil forest. They 
are merely the roots of trees which once grew in the 
swamps. The black peaty cementing material in the 
Tweed Heads area has been analysed, and its organic 
nature definitely established. 
IGNEOUS INTRUSION. 
Of the greatest geological interest is the intrusion of 
porphyrites and aplites into the Mesozoic ( Jurassic ) 
sediments. In New South Wales, Victoria, Tasmania and 
South Australia major igneous intrusion is not known to 
occur after the Palaeozoic era. . In South-Eastern Queens- 
land we have at Enoggera, Stanthorpe, Cedar Creek, Sam- 
i'ord and elsewhere late Palaeozoic intrusions, and it is 
important therefore to find at Coolum and at Noosa de- 
finite evidence of intrusion into the still younger Mesozoic 
:sediments. 
At Pofnt Arkwright, sandstones which have been 
baked by heat into quartzites are seen resting immediately 
on top of the porphyrites and sections in the wave -cut 
platform show the intrusion of the porphyrite right into 
the sediments. The evidence is beyond question here, as 
at Noosa. 
Where the heat of intrusion has been greatest the 
sandstone has been altered to quartzite, but the thickness 
of affected material is a few feet only. In the intruding 
porphvritic rocks are many inclusions, and one agrees 
with Jensen as to the laccolitic character of the igneous 
mass. Many undigested fragments are incorporated in 
the upper part of the intrusion, but in addition there are 
many Xenoliths which have been brought through from 
below — notably amongst these are fragments of (a) coarse 
pink granitic rock of a type which is unknown to 
geologists in S.E. Queensland nearer than Stanthorpe; 
(b) coarse grey granitic rock similar to those exposed in 
the Mary River Valley near Conandale. The evidence of 
coarsely crystalline deep-seated intrusives having been 
penetrated by the porphvritic mass on its upward path is 
clear, and in this way some insight of what may exist at 
depth in this area is furnished. 
The porphyrite is rich in well-developed phenoerysts 
of plagioclase and hornblende, the latter being occasion- 
