BY H. I. JENSEN. 565 



referred to in my papers on the Warrumbungle and Nandewar 

 Mountains. In the Parish of Benolong Mr. Murton has also 

 collected specimens of nepheline phonolites described by Mr. Card 

 as Miaskose.* 



On my own visit to Dubbo I found near The Gib a formation 

 of quartz porphyry (granite) which probably belongs to the 

 Palaeozoic, but Post-Silurian series of igneous intrusions. It has 

 no affinities at all with the alkaline rocks which in places intrude 

 it. The Triassic strata of this region are fairly thin and rest 

 on the quartz porphyries mentioned, and on Palaeozoic schists 

 belonging to the Cobar massive. They thicken towards the 

 north and north-east, where they overlie the Upper Coal Measure 

 formation; possibly their greater development in the Warrum- 

 bungle area may be the downthrow by a peripheral faulting of 

 the whole area lying within the curve of the Castlereagh. 



In travelling across country from Coonabarabran via Mundooran 

 and Cobborah to Dubbo I noticed that very frequently the 

 summits of the ridges crossed consisted usually of sandstones and 

 conglomerates of the Triassic facies, whereas the formation in 

 the valleys consisted of sandstones and shales of the Permo-Car- 

 boniferous type, giving a more clayey and fertile soil. In the 

 valley of the Talbragar Triassic beds are also found in erosion 

 hollows in the Permo-Carboniferous formation. 



The Warrumbungle Mountain s. — The geology of 

 this group I have discussed more fully elsewhere, f 



The Warrumbungle mass commences a little over 50 miles north 

 by east from Dubbo, and is situated on a line of weakness which 

 pursues a N.N.E. or N. by E. direction from Dubbo to Narrabri. 

 All along this line alkaline rocks are met with. 



The physical features and land-forms of this area are described 

 in my paper (loc. cit.). The volcanic mass is looked upon as a 

 dissected lava-conoplain, and the surrounding country to the south- 

 east, south, west and north as an arid-cycle peneplain. I had an 



* "Mineralogical -Notes," by G. W. Card, No. 10, Records Geol. Surv. N.S. 

 Wales, Vol.viii., Part 3. 



t These Proceedings, 1907, Vol.xxxii. p.557. 



