814 



DIAMOND-DEPOSITS OF COPETON, N.S.W. 



Cope's Creek. Tins explanation, moreover, implies that, at the 

 period of basaltic intrusion, this block-faulted area was at a much 

 higher elevation, and, consequently, more likely to have escaped 

 being flooded with lava; and it has been pointed out that no 

 evidence of basalt was found on this area. 



. It thus appears probable that the Gwydir is a post-basaltic 

 stream, which has followed the direction of the two faults bound- 

 ins: the north-east corner of a fault-block.* 



The reconstruction of the pre-basaltic physiography, then, 

 involves the elevation of the fault block into its original position. 

 If we suppose this to be done, there remains only the removal of 

 the basalts to restore the conditions of the pre-basaltic physio- 

 graphy. The presence of river-gravels, and of V-shaped sections 

 of basalt lying on granite-foundations, enables a large amount 

 of this imaginary construction to be readily performed. 



The final result of this re- 

 adjustment of the efi'ects of 

 natural processes transforms 

 the area into a denuded pene- 

 plain at an elevation of 3,000 

 feet above sea-level. The dis- 

 cussion on the disposition of 

 the Tertiary leads indicates 

 that the pre-Tertiary streams 

 united to form a north-flow- 

 ing river. This tendency of 

 the pre-basaltic drainage to 

 flow north is in marked con- 

 trast to the present trend, 

 Text-fig. 2rt --Map showing the Tertiary which is towards the west. 



and Recent river-systems of the From the junction of Au- 

 Gwydir and Macintyre near ^^^^^ y^j^ ^^^^^ ^-^j^ ^^p^,^ 



Creek, a broad basalt-flow 



trends northwards towards the western side of the town of In- 



verell. For about half the distance, the flow is limited on each 



side by granite; but, near Inverell, only the eastern boundary is 



* Farther evidence of faulting occurs to the west at Keera Station. 



C rj n I ^c 



DID Basjif 



