BY H. 1. JEXSE.V, 843 



The region is, from a geological standpoint, practically 

 unexplored, though parts have been visited by Mr. E. F. Pittman, 

 A.R.S.M., Government Geologist; and by Professor T. W. E. 

 David, B.A., F.R.S. His Honor Judge Docker has visited 

 practically all parts of this region to take scenic photographs, and 

 is probably better acquainted with it than anyone who has made 

 casual trips to it. 



2. Petrography. 



The rocks of the Nandewar Mountains may be conveniently 

 divided into Sedimentary, Metamorphic, and Igneous. 



The Sedimentary Rocks include (a^ Carboniferous conglomerates 

 and grits, chiefly in the S.E. and E. portions of the area; 

 (b) Permo-Carboniferous conglomerates, grits, sandstones and 

 shales, forming the country rock in the area where volcanic 

 activity has been greatest. The Permo-Carboniferous rocks 

 continue westward under the plains, and are also the most 

 important formation in the Rocky Creek district.^ (c) Trias-Jura 

 rocks, forming mesas capping the Permo-Carboniferous. 

 (d) Tertiary deposits. 



The Metmnorphic Series includes (a) slates, cherts and schists 

 of Devonian age associated with the Carboniferous rocks in the 

 S.E. (at Coolah Station), (b) The limestones and serpentines in 

 the Horton River basin, east of the Nandewar Mountains, out- 

 side the district which I have myself examined. 



The Igneous Rocks comprise (a) granite, as rolled boulders in 

 Maule's Creek. 



(b) Akerite, occurring as laccolitic bosses and sills at the head 

 of Bullawa Creek. Also tegirine-nepheline syenite, forming 

 sills in the same region. 



(c) Sills of syenite-porphj^ry and bostonite. 



(d) Trachyte, phonolite and rhyolite, with all kinds of 

 texture, from aphanitic and even-grained to coarse and 

 porphyritic, and from compact to highly vesicular. These 

 rocks occur as lava-flows or cappings, dykes and sills 

 throughout the area extending from Deriah Mountain on the 



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