260 
The present paper is limited to a description of the three 
upper members of the series, with special reference to their 
development in the Field River and Onkaparinga districts. 
(A) Purple Slates. 
It is convenient to adopt this heading for a great series 
of slates, shales, flaggy sandstones, quartzites, and limestones 
which are more or less distinguished by a dark purple or 
chocolate colour. There is apparently no stratigraphical 
break between the Brighton limestones and these dark- 
coloured beds; but the lithological distinction between the 
two divisions and the superposition of the purple slates are 
clearly defined. The fact that these beds are mostly sub- 
merged by the waters of the Gulf, in the neighbourhood of 
Adelaide, no doubt accounts for the fact that they have not 
been studied to that extent which their importance demands. 
In the sea cliffs between Marino and Hallett’s Cove, as well 
as on the beach, planed down by the sea, it is easy to recog- 
nise the marked contrast which these beds present to any 
others on their eastern side. Dark-purple slates, sometimes 
chloritie, splitting up into small flakes and prismatic pieces, 
line the coast. The cliffs are almost on the line of strike, 
and expose the waste of & great anticlinal fold facing the 
sea. Interstratified with these dark shales will be found very 
hard-grained and dark-coloured quartzites, often divided up 
into thin beds and !aminz, and a few similarly coloured, thin 
limestones, hardly to be distinguished from the associated 
argillaceous beds, and often indicated by containing white 
veins of fibrous calcıte. 
At Marino these beds һауе a breadth of barely half a mile 
before they pass below sea level, to re-appear on Yorke's 
Peninsula as the Archwocyathine limestones, underlain by 
purple slates, etc., as on the eastern side of the Gulf. These 
beds, inferior to the fossiliferous limestones, have been prov- 
ed in the Maitland bore, they outerop on the Winulta Creek, 
and are seen in the railway cuttings between South Hum- 
mocks and Kulpara. Characteristic exposures of these beds 
occur at Black Point, on the north side of Hallett's Cove, 
where they have been intensely glaciated; and on the lower 
Onkaparinga, at the Horseshoe, where they formed the old 
sea cliffs of Miocene age. Along the line of strike, between 
Field River and Curlew Point, about three miles south of 
Hallett's Cove, there has been a zone of extreme pressure and 
contortion, with overfolding of the beds. Some excellent 
photographs of these features, taken by Mr. J. Greenlees, 
accompany this paper. (See Plates xxxvii.-xlii.) 
