XXX. ABSTRACT OF PROCEEDINGS. 



Mr. E. O. Andrews delivered an address : — 



Periods of Folding and Ore Deposition in Australasia 



t 

 and the Associated Islands. 



1. With the progress of geological time the great periods of 

 folding in Australasia retreated from the south-west in directions 

 both easterly and northerly. The periods of ore deposition were 

 intimately associated with certain of these periods of folding with 

 the possible reception of the Waihi and associated fields in New 

 Zealand, which appears to have been related to volcanic eruptions. 



2. According to Maitland, the great bulk of the plateau of 

 Western Australia appears to consist of crystalline schists and 

 other highly altered rock types, associated with plutonic masses, 

 the general strike of the series being north-west and north-north- 

 west, all being Pre-Cambrian in age. Howchin, David, Carne 

 and others, have described the Cambrian and Ordovician as having 

 a general north-westerly and north-north-westerly trend from 

 South-eastern Australia (south of Sydney, to the north of the 

 Northern Territory. In detail, however, these folds have immense 

 corrugations developed along their general direction of strike. It 

 is possible that this period of folding belongs to the close of the 

 Ordovician. During the Silurian and Devonian times, the Epi- 

 continental seas were greatly extended, and they encroached as 

 far west as the Darling River in New South Wales near Bourke. 

 Both these periods appear to have been closed in Australia with 

 strong folding. A great zone of weakness with a strike almost 

 north-north-west and, stretching from Sydney beyond Narrabri, 

 appears to have divided New South Wales, if not indeed, Australia, 

 into two distinct geological provinces, about the Devonian or 

 earlier period. West and south of this zone, the area of Australia 

 does not appear to have been affected by strong folding movements 

 since the commencement of the Carboniferous, but north and east 

 of this zone, according to Benson, the Devono-Carboniferous 

 sedimentation appears to have been closed by a strong movement 

 of folding, while farther east and north again, the Permo-Car- 

 boniferous sediments appear to have been folded strongly along 



