566 THE GEOLOGY OF THE WARRUMBUNGLE MOUNTAINS, 



The Warrumbungle Mountains are drained by the tributaries 

 of the Namoi and Castlereagh Rivers. The former is a con- 

 sequent stream, throughout most of its course following the dip 



Black mt^t 



DGElb 



jZb5bj[h 



^lue Phonoiltic 



Fig.5. 



Vesicular 

 Tracj vy^ Tu.[f • 



V ~ 



Sandstone 



(Dl^6w) 



-Diagrammatic Section showing the structure of Goat Mountain, 

 Tannabar. 



of the Trias-Jura (or Trias) rocks in a N.N.W. direction. Pro- 

 bably it is a very old river, as Mr. E. C. Andrews has pointed 

 out,"^ originating in its present course when the Triassic sediments 

 were tilted in Cretaceous time. It follows that, where these 

 sediments have been denuded away and the Namoi runs through 

 Permo-Carboniferous rocks dipping S.W., it occupies a subsequent 

 position, and is in reality a supe7'imposed stream. In some 

 places it cuts through deep alluvial plains of its own deposition, 

 as at Narrabri. Many of its tributaries are subsequent streams 

 running N.E., following the strike of the Trias-Jura. The Namoi 

 is older than the raised peneplain marked by the mesas of Coona- 

 barabran. The erosion produced by tributaries like Brigalow 

 Creek, Baradine Creek, Bohena Creek and Bugaldi Creek has 

 given rise to similar mesas of about the same altitude in the 

 Pilliga Scrub, north of the Warrumbungle Range. 



The Castlereagh rises in the Warrumbungles near Mobara. 

 First it pursues an easterly course through a wide gorge or 

 valley, with steep cliffs bounding it on the north. A few miles 



* " Tertiary History of New England," Eecords Geol. Survey N. S.Wales, 

 Vol. vii. 1903, p.27. 



