By C. Fenner, D.Sc. 
131. 
fS.A. NAT., VOL. XIV. 
August 31st, 1933. 
Looking again at the diagram we see first of all the Adelaide 
Plains with the ancient bedded rock deep below, the Miocene 
limestones buried out of sight, the Pleistocene muds only coming 
to the surface at Brighton and Seacliff, the later alluvium and 
^sand-dunes covering the surface. 
To the south is the uplifted and tilted block of O’Halloran 
Hill, crossed in its southern part by the Onkaparinga River, which 
■enters the sea of Port Noarlunga. The Onkaparinga has carved 
a valley through the hard rocks of the adjoining uplifted block 
to the south. The third block is equally tilted to the south and 
east and the over-lying limestones and mudstones increase as 
we approach Sellicks Hill. 
The uplifted scarp face of the Sellicks Hill block forms the 
Willunga Ranges, and is one of the chief barriers towards com- 
munications between Adelaide and the southern districts. It 
has effectively prevented the passage a\ a railway, which stops 
short at its base. The new bituminous road round the seaward 
base of Sellicks Hill circumvents this powerful barrier in a fairly 
■effective manner. 
Perhaps the most interesting correlations that can be made 
in this strip of country are those between the geology, tne land 
forms, the drainage type and the native vegetation. These re- 
lations are very close indeed, and they prove to be very interest- 
ing where they have been worked out. A Inch systematic work 
remains to be done by the combined effort of the physiographer 
.and the botanist, or better still, b}' an alert field naturalist who 
■combines a simple but correct knowledge of the geolog)’^ and land 
forms with an eye for drainage and with sufficient botanical train- 
ing to collect his specimens wisely. 
A brief note will novv be given of the more important physio- 
graphic features along the coast. 
Mud Flats.— These are in areas where cstuariiie muds 
£iVQ being brought down from the uplands and where winds and 
tides have no power to build up sand-dunes. The chief mud 
[lats are near the mouth of the Port River and the Northern Arm, 
where there arc beautiful mangrove-fringed reaches river 
backed by ugly mud flats. A second area of mud flats occurs 
in the tidal portion of the Onkaparinga where mangroves are 
.less common. 
Sand Dunes. — The main stretch of san(l dunes is that 
from Outer Harbour to Seacliff. The dunes are here of two 
types. From a little north of Largs to Seacliff the dunes have 
been built up in a succession of long ridges, dune and swale, 
usually three in number, but all the upper part of Le Fevre Pen- 
insula has been .built up differently. Here the sand dunes were 
