PRESIDENTIAL ADDRESS. 15 



'Geological Department, at the Sydney University, from 

 petrographical data. This fault has a surface displacement 

 exceeding 1,000 feet. It is expected that the geological 

 survey of the area will result in the location of several 

 important "strike" faults within the Pinnacles-Broken 

 Hill-Round Hill area. These faults have an important 

 relation to the Broken Hill ore bodies. 



About fifty miles to the north-west of Broken Hill the 

 rock outcrops are suggestive of silicified sandstones and 

 shales, and with these are associated an abundance of 

 ironstained nodules of flinty appearance with masses of 

 compacted sand and with abundant traces of opalised wood. 

 It is reported that similar occurrences are to be seen closer 

 to Broken Hill to the north-west. By analogy with the 

 appearance of the rocks in the White Cliffs district these 

 sediments appear to belong to the Cretaceous period. The 

 present surface is that of a plain of denudation with out- 

 liers of Cretaceous sediment. 



2. Cobar District. — Just as Broken Hill is the great 

 centre of the lead-zinc-silver production, so the Cobar 

 district has been the great centre of the copper industry 

 of the State. The rocks in which the copper occur are not 

 so old as those containing the lead, silver and zinc of Broken 

 Hill ; nevertheless, they appear to be Lower Palaeozoic in 

 age. Each lies within a low plateau or shield of old rocks 

 having a trend somewhat north and south, the Cobar rocks 

 west of north, and the Broken Hill types east of north. 

 The two districts are separated by the wide area of the 

 Darling River alluvium. The lodes of Cobar appear to lie 

 within subparallel and overlapping crush zones from Mount 

 Hope one hundred miles south, to the C. S. A. Mines, seven 

 miles north-north-west of Cobar. 



The commercial ore bodies occur as lenses within these 

 crush zones, and the known bodies are only payable at 



