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



basaltic period; to remove the basalts entirely; simultaneously to 

 readjust, in their proper chronological order, the results due to 

 earth-movements; there would then appear, in its original state, 

 the topography of the pre-basaltic period. 



Mr. E. C. Andrews has given an excellent general account of 

 the physiography of northern New England. He has shown 

 certain stages of peneplanation, the youngest of which has left 

 its record as the Stannifer peneplain; and the physiography of 

 Copeton is dominated by this feature. 



A study of the contours on the accompanying geological map 

 reveals three topographical units. These are : — 



(1). A relatively low-level area bounded, on its north and east 

 sides, by the Gwydir River. This is about 2,200 feet in height. 



(2). An area of moderate relief situated north of Copes Creek 

 and the Gwydir. This area has an altitude of about 2,800 feet. 



(3). An area of relatively high relief situated to the east of the 

 Gwydir, and to the south of Cope's Creek. This area attains an 

 altitude of as much as 3,400 feet. 



The first of these is wholly in the Oakey Creek granite-area. 

 I examined about one hundred square miles of this area, but 

 failed to obtain any evidence that it had been covered by basalt. 

 If such has been the case, denudation has removed all trace of 

 the lavas. The channel of the Gwydir is about 200 feet below 

 the general level of this area. 



The second unit presents more variety in its geological struc- 

 ture. The basal rock is granite. Two types — the Oakey Creek 

 granite and the Acid granite — are present^ and these are separated 

 approximately by a tributary of Copes Creek (see Plate xcii.). 

 There are also masses of clay-slate included in the area, mainly 

 to the east of the Auburn Yale Creek. Basalt overlies a con- 

 siderable portion of each of these rocks. This area represents 

 the denuded surface of the Stannifer peneplain. 



The third unit is composed of the Acid and Tingha granites, 

 and basalt has been found only along old valleys cut in these 

 structures. This area also represents part of the original Stanni- 

 fer peneplain. Further data are yet required for the solution of 

 the problem. These are supplied by a knowledge of the positions 



