188 president's address — section c. 



17.— THE FAULTING DUE TO THE LATE TERTIARY UPLIFT IN 

 EASTERN AUSTRALIA. 



By E. C. ANDREWS, B.A., F.G.S. 



18— PRE-CAMBRIAN AREAS IN THE NORTH-EASTERN PORTION 



OF SOUTH AUSTRALIA AND THE BARRIER. NEW SOUTH 



WALES. 



By D. MAWSON, D.Sc. 



[plates XV., XVI.] 



At the Adelaide (1907) meeting of the Australian Association for the 

 Advancement of Science I communicated a paper defining the age 

 as Cambrian of a series of sedimentary rocks flanking the older 

 schistose and gneissic areas of the Barrier Ranges, N.S.W. In 

 places this series was noted to be highly metamorphosed, thus com- 

 plicating the work of distinguishing older formations. Several 

 sections in the Barrier Ranges were noted which strongly favoured 

 a pre-Cambrian age for the major portion of the granite and meta- 

 morphic belt. More conclusive, however, is the data furnished in 

 the neighbouring portions of South Australia, where the strati- 

 graphy is similar. Evidence is now available to show that there 

 are larger areas of pre-Cambrian rocks in the north-eastern portion 

 of South Australia, even crossing the New South Wales border in 

 the vicinity of Broken Hill. 



In a recent thesis^ on this area I have distinguished the pre- 

 dominant formations as the " Torrowange Series " (Cambrian) and 

 the " Willyama Series " (pre-Cambrian). The object of this con- 

 tribution is to place on record the two sections shown in the accom- 

 panying plates. The evidence incorporated therein definitely 

 determines the existence of pre-Cambrian areas and assigns that 

 age to the Willyama Series. 



The first of these sections (Plate I) refers to the neighbourhood 

 of Olary. This is in South Australian territory, at no great distance 

 west of Broken Hill. In this vicinity I have followed the junction 

 of the Cambrian and pre-Cambrian rocks for many miles. The 

 section given is semi-diagrammatic, illustrating the stratigraphy 

 near Bimbowrie head station, some 15 miles north of Olary. There 

 a syncline of Cambrian sediments lies between and rests upon a 

 pre-Cambrian basement. This syncline is about 3^ miles across. 



The pre-Cambrian terraine consists chiefly of a ternary granite 

 of medium grain size, and of gneissic and schistose products resulting 

 from the dynamo-m.etam.orphism of the same. Even the least 

 altered granite shows the effects of stress when examined in micro- 

 scope sections. Basic ilmenitic pegmatites and acid beryl-bearing 

 pegm.atites are features of the pre-Cambrian areas. Somewhat 



1 Now in process of publication. 



