414: PROCEEDINGS OF SECTION C. 



8.— A GENEEAL DESCRIPTION OF THE CAMBRIAN SERIES 

 OF SOUTH AUSTRALIA. 



% WALTER HOWCHIN, F.G.S., Lecturer in Geology and Palaeontology in the 

 University of Adelaide, 



For some time great uncertainty existed as to the geological age 

 of the Mount Lofty and associated ranges. The late Professor Tate 

 regarded them as exclusively Archsean, limiting the Cambrian areas 

 to an outcrop near Ardrossan, Yorke Peninsula, and certain portions 

 of the Flinders Ranges, indicated by the presence of Archceocyaihince. 

 Mr. H. Y. L. Brown, in his Geological Map of South Austraha (1899), 

 indicates in descending order from west to east — (1) Cambrian and 

 Lower Silurian (?), (2) Cambrian, &c. (Metamorphic), (3) Metamorphic 

 and Plutonic. Until recently the data at command were insufficient 

 to define the Cambrian areas in their true extent, or the recognition 

 of a Cambrian base level. 



Sufficient detailed work has now been done to give a generalised 

 description of the great Cambrian system of South Australia, which, 

 so far as the south-central highlands of Australia are concerned (includ- 

 ing the Mount Lofty, Barossa, Flinders, and other ranges), is by far 

 the dominant geological feature of the country. No other Palaeozoic 

 formations occur within the areas indicated, unless we take into account 

 the glacial beds of the Inman Valley and Hallett's Cove, which are 

 probably of Permo-Carboniferous age ; and the Pre-Cambrian exposures 

 are of limited extent, mostly lineal and following the main axis of the 

 ranges. 



The Cambrian series is of very great thickness, probably not less 

 than 30,000ft. to 40,000ft., or even more. So far as known, the beds 

 are conformable throughout. The most clearly marked hthological 

 •distinction in the series occurs about the horizon of the Brighton Hme- 

 stone. Above this horizon the typical characteristic is that of red- 

 colored rocks, chiefly purple slates, quartzites, and sandstones. Below 

 the Brighton limestone the rocks consist principally of slates, siliceous 

 quartzites, phyllites, and one or two limestones. In this lower part 

 of the system there are no purple slates, and the rocks are not colored 

 red. The transition at the Brighton horizon is certainly somewhat 

 sudden and strongly marked ; but it is not clear that an unconformity 

 exists. There seems, indeed, to be a transition zone of color, for the 

 upper bed of the Brighton limestone is reddish and is locally known 

 as the " pink limestone." 



Upper Cambrian. 

 The close of the Cambrian period was marked by a great elevatory 

 movement that initiated the main physiographical features which 

 have, in a measure, persisted to the present day. The evidence (so 



