269 
A little south of the Field River there is an extensive floor 
of marine denudation produced by planing off the purple 
slates, which exhibit parallel lines of outerop on the beach. 
The lines give a very clear exposure of the bedding along Ше 
Strike, and, when the tide is out, a remarkable example of 
à strike overfold is seen in the form of a very extended letter 
<>. It can be seen to best advantage from the top of the 
cliffs. 
The most striking illustrations of the acute foldings which 
occur in these beds are found at Curlew Point, about three 
miles south of Hallett’s Cove. (See Plates xxxix.-xlii.) 
The purple slates pass out of sight below sea level, with 
а dip to the west. The waters of the gulf occupy a deep 
valley cut in these beds; in the first instance, possibly, by a 
river which had its watershed in highlands to the south of 
the present continent, and its outlet to the north. These 
southern highlands were in existence, as a watershed, during 
the (?) Permo-Carboniferous glaciation of the southern por- 
tions of Australia, and must have been, even at that time, 
of considerable elevation and extent, to produce å ground ісе 
of such magnitude as to fill the valley of the gu!f and over- 
lap the adjoining land. The purple slates re-appear on the 
other side of the Gulf, where they are relatively thin, and 
rest on Pre-Cambrian beds. They are overlain by thick 
limestones at Curramulka, Ardrossan, Maitland, Clinton, 
Kulpara, etc., which contain characteristic fauna of Lower 
Cambrian age. 
IV. THE ONKAPARINGA SECTION. 
Introduction.—The Onkaparinga River flows through a 
Sorge which is, perhaps, the most inaccessible эпа roughest 
in the southern portions of the State. Between Noarlunga 
and Clarendon the sides of the valley rise abruptly from 300 
to 600 feet in height. About two miles from the coast the 
“iver suddenly leaves the highlands and enters the plain, 
forming a pieturesque loop known as the “horseshoe,” within 
the limits of which the township of Noarlunga is built. At this 
point the river has reached its base level, the water being 
tidal on one side of the narrow neck of land and fresh on 
the other. From Noarlunga to the sea the river follows a 
tortuous course, with alluvial, estuarine, or tertiary banks, 
which continue to its mouth. Deep as is the gorge of the 
Tlver it is evident it must have been cut since later Miocene 
times, as deposits of this age cap the hills on both sides of 
the river. It is possible that in pre-Miocene times the river 
had lts outlet by Maclaren Vale, which is now choked with 
Miocene deposits. High-level gravels of the river bed can 
* Seen at Noarlunga, near the top of the Church Hill, on its 
Western side. 
