June 1947 The Queensland Naturalist 
45 
to the west of the “granite” mass, there is a swarm of 
andesite dykes; near to the “granite” and to the east 
of it is a series of aplite veins. A compound dyke is 
filling a joint plane in the quartzite, forming the cliffs 
at Noosa Heads; an andtsite dyke occurs inside a horn— 
blende-porphyrite dyke. Another hornhlendc-porphyrite 
dyke occurs in the headland at the south end of Alex- 
andra Bay; while an andesite dyke is seen just south of 
the Paradise Caves. 
In the Council Quarry, above the Xoosa settlement, 
several hornblende porphyrite dykes are seen in the 
vicinity. 
The ages of the “granite” and the hornblende 
porphyrite are unknown, but are probably Mesozoic No 
rhyolitic or trachytic dykes were seen at Xoosa. 
Perhaps the movement which tilted the sediments on 
the road west of Ttwantin accompanied the intrusion of 
the “granite.” 
The Tertiary era is represented by the great plug of 
an ancient volcano, whose outer cone has weathered away 
— the trachyte dome of Mt. Tinbeerwah, which pierces 
the Mesozoic sediments to the north of the Cooroy- 
Tewantin road. This particular plug is an especially inter- 
esting type of trachyte, with large phenocrysts of biotite. 
and some smaller ones of augite or hornblende. Although 
there are many other trachytic volcanic plugs of Tertiary 
age in coastal Queensland, such as the Glass House Moun- 
tains, only one other is known with a similar biotite 
trachyte, and that is Mt. Lawless, near Gayndah. Other 
plugs of this ana are Mt. Coolum, Mt. Perigian. Mt. 
Pinbarren and Mt. Cooroora. Possibly the rhyolite or 
trachytic dykes and sills seen on the road belong to the 
same Tertiary period of igneous activity as these plugs. 
Post-Tertiary time saw a mantle of wind-blown sand 
deposited on the quartzite of the Noosa high land ; hut 
the most extensive deposits formed in this recent period 
are those forming the flat marine plains between the salt- 
water Lakes Weyba. Doonella, Cooroiba and Cootharabah. 
These plains are only a few feet above sea level, and parts 
are inundated at king tides. They are almost level and 
in their natural state carry a close cover of vegetation. 
It has been suggested that the area of these plains end the 
lakes was formerly entirely inundated by the sea, and 
that a recent emergence of the land of the order of a 
