11 
lhe whole of this dime area is covered with vegetation ; grasses near the coast with 
Casuarina and Banks ia. patches of mangrove in swampy areas, larger eucalypts and other timbers, 
often fine, well-formed trees, inland. The history of the area seems to have been as follows 
For some reason or other, possibly a change in tlie elevation of this part of the coast, the causes 
leading to the formation of the sand dunes became weakened. Grasses and other dune plants 
took hold in the loose sand and tended to form both humus and a protecting cover. As humus 
developed, Casuarina, Banksia, and other small scrub obtained a footing, iron began to concentrate 
around the plant roots, and some cementation of the sand grains resulted. I'ims the protection 
afforded by the cover of vegetation became more and more permanent and effective, until the 
dunes became fixed and little affected by wind and rain, and forest trees from the landward side 
gradually encroached upon the area. As sand dunes they were then dead, and had become more 
or less permanent deposits. 1 have described these conditions in some detail because they have 
a bearing upon our problem. 
Examining the cliff sections along the coast we find that they consist almost entirely of 
fine-grained loose sands, sometimes partly cemented with iron which, in various stages of hydration, 
shows itself in stains of brown, pinks, and reds of various shades, so that they are known locally 
as the “ Painted Sands/' Where the forest and scrubs have taken hold in the surface beds the 
sands contain humus and organic matter, and the colour becomes a dark sooty brown. Mr. Ball 
thinks that this colouring is due to forest fires. Such fires would, of course, augment the supply 
of carbonaceous material, charcoal, sooty matter, and ash in the covering beds, but the ordi ary 
phenomena of growth and decay and the wear and tear of the life of the scrubs and forests would 
bring about the effects noted. Traversing the area from east to west, we found that the surface 
sands below the trees show universally this dark and dirty colour due to the presence of humus 
and carbonaceous matter. Where such accumulations have been in excess of the average, and 
have been protected, as in water- logged depressions, dirt beds are formed which may be covered 
by fresh encroachments of sand in any revival of activity in dune formation sometimes accom- 
panying oscillations in the land levels. Such beds are to be seen in the sand-dune areas of 
South Australia, and in the dune areas around the estuaries of the Dee and the Mersey in England . 
The sands show rough, irregular stratification typical of such deposits. Some of the beds appear 
to be folded into low anticlines and synclines when traced along the beach cliffs for some distance, 
but I consider this to be due entirely to the shifting character of dune formations. Both hills and 
valleys “ walk,” so to speak, in the direction of the prevailing winds when the dunes are “ living ” 
things. Dunes are really wind ripples on a large scale, and cliff sections show stages of growth 
and rest, old troughs and crests. The rythmic effects of wind action is shown in these cliff sections 
just as it is on a smaller scale in a piece of ripple-marked sandstone affected by the action of water 
the wave motion of which produces similar effects. 
Just south of the andesite mass of Double Island Point the coastal cliffs are formed of a 
different type of deposit. More or less we 11 -stratified beds of rather well-consolidated calcareous 
grits lie against the lavas and apparently dip at a low angle to the south. The beds consist of 
sand grains and broken shell fragments. They are typical beach deposits — a mixture of wind-blown 
sand and comminuted shell fragments such as accumulate under the action of wave and wind 
on reef-fringed shores. We found nothing to indicate the age of these beds. They appear to 
have been elevated somewhat by a rise of the Double Island Point mass, and to have formed the 
beaches around that mass when it was at a lower level with regard to the sea. Such material 
was probably carried by tidal scour from neighbouring coral shoal areas and deposited against 
the obstructing mass formed by the igneous rocks, such accumulations in a shallow and rising- 
channel eventually linking the old islands with the sand dunes of the coast. In the absence of 
any evidence to the contrary, 1 regard these beds as contemporaneous with the old sand-dune 
formations. 
The boreholes have proved that the soft, fine, consolidated sands of the old dune formation 
exist to a depth of approximately 200 feet below sea level. This proves that this part of the 
coast-line has been depressed to this extent in Post-Tertiary times. While such a depression of 
the coast-line might cause some sagging of the beds between Double Island Point and Noosa Head, 
that could only occur if the igneous masses at those points had not sunk to the same extent as 
the rest of the coastal fringe. There is evidence that subsidence has affected the whole of the 
coast of Queensland in Post-Tertiary times. The movement is really part of extremely slow 
oscillations, evidence of which is often to be found on continental margins. At present we know 
too little about the areas affected to say very definitely whether the movement is uniform or whether 
it varies according to the nature and age of the rocks which are the fundamental beds of any 
particular part of the coast. In any case, I should not expect to find that such movements were 
accompanied by such lateral pressures as would cause incipient folding in the soft surface strata 
of Post-Tertiary age such as those with which we are dealing. 
