846 THE GEOLOGY OF THE NANDEWAR MOUNTAINS, 



valleys, with steep, often precipitous, walls on each side. The 

 cliifs usually expose sandstone up to a certain height (about 

 2,000 feet), above which we find flows of trachyte. Both in a 

 N.N.W. and in a S.S.E. direction from Mount Kaputar the 

 axis gradually declines in altitude; so that, at the head of 

 Bobbiwaa Creek it averages only about 2,500 feet; and at the 

 head of Oakey Creek (Coolah Station), a branch of Maule's 

 Creek, its height is 2,400 feet, though peaks of higher altitude are 

 met with on the chain. 



The Black Soil Plains surrounding the Nandewar Mountains 

 resemble those already described for the Warrumbungles. They 

 may be either with or without forest. The commonest trees on 

 the forested black soil plains are box {E. hemiphloia var. albens, 

 and E. Woollsiana), apple trees {Angophora intermedia), ironbark 

 [Eucalyptus crehra), oaks [Casnarina Cunninghamii and C. 

 Camhagei) along w^atercourses or plains of alluvial origin; and 

 box {E. hemiphloia var. alhens), with myall {Acacia peiidula), 

 ironbark (E. melanopJiloia), wattles {Acacia), when black soil is 

 purely of volcauic origin as at Bobbiwaa Creek. 



The Pilliga Scrub adjoining Narrabri at Turrawan answers to 

 the description already given of other parts of the same area. 

 It consists or a thick pine {Callitris calcarata) jungle with occa- 

 sional ironbarks {Eucalyptus sideroxylon) and wattles inter- 

 spersed, growing on deep white or yellow sand. The lower 

 branches of the pines exhibit a remarkably even skyline, due to 

 a process of natural pruning which is better illustrated here than 

 at any other spot which I have seen in Australia. Patches of 

 poor sandy country of the Pilliga type occur also between Maule's 

 Creek and Boggabri. Here it is very undulating, capped with 

 table-topped hills (mesas) of conglomerate and sandstone which 

 are probably of Trias-Jura age. These mesas would, if their tops 

 were continuous, form an inclined plane sloping awa}^ from the 

 Nandewar Mountains. In this way, too, the mountains descend 

 into the plain in a southerly direction. In the Parish of ISTamoi, 

 County Darling, they run into the JSTamoi River and disappear. 

 Around Boggabri and west of this township the country would be 



