570 THE DISTRIBUTION, ETC., OF ALKALINE ROCKS, 



Commencing at Kiama, the line runs N.W. to Orange, thence 

 N.N. W. to Dubbo, thence N.N.E. to Narrabri. The whole of 

 the area within the curve probably remained stationary in the 

 Eocene following upon its long period of elevation in Cretaceous 

 times. Certain areas like that lying between the New England 

 massive (bordered by the N.N. W.-S.S.E. fault of the Nande- 

 wars), and the Cobar massive probably were completely severed 

 by intersecting fractures and formed subsidence-areas. A high 

 mass of Palaeozoic rocks, probably a horst, the Bathurst- Welling- 

 ton mass, borders the Gunnedah Basin on the south. 



The fault-line along which alkaline rocks have been erupted 

 universally divides the outcrops of ancient Palaeozoic rocks, which 

 formed the late Palaeozoic and early Mesozoic land-masses, from 

 the Mesozoic and Permo-Carboniferous sediments which were 

 pinched between them, and in some parts folded. The alkaline 

 lavas are not found in the centres of sedimentary basins like New 

 England and the Sydney Basin, but only along the fractured 

 continental borders of Mesozoic seas and their continental shelves, 

 where slight transgressions of the sea occurred at intervals. 

 Folding is nowhere intense, but fracturing has been considerable 

 in Tertiary time along the line. 



Incidentally the Dubbo-Narrabri line happens to be parallel to 

 the line of strike of the Mesozoic sediments of the Gunnedah 

 Basin, and consequently is at right angles to the direction in 

 which the uplifted Mesozoic has been gently pushed (or folded). 



The main importance of the line, however, lies in the fact that 

 it is a line which was a shore-line throughout late Palaeozoic and 

 Mesozoic times. In the Carboniferous the continental area lay 

 to the west of it and the sea to the east. In the early Permo- 

 Carboniferous a portion of the area comprising the Gunnedah 

 Basin was elevated, and at the end of the Permo-Carboniferous 

 when the New England area emerged, this same portion became 

 resubmerged, probably as a vast lake. In the Mesozoic the 

 Kiama-Dubbo segment of the curve still remained with land to 

 the west and sea to the east, but the ;Narrabri-Dubbo portion 

 had land (New England) to the east and sea (the Cretaceous) 



