BY H. I. JENSEN. 871 



be found to be Trias-Jurca. In the first place, most of the sand- 

 stone between the Castlereagh Kiver and the Warrumbungles 

 has the appearance of being Tiiassic. The range lying between 

 the Castlereagh and the Talbragar Rivers is probably also 

 Triassic, the valleys only belonging to the Coal Measures. 



Around Dubbo, to which I drove from Coonabarabran via 

 Mundooran and Cobborah, there are Triassic rocks containing 

 good imprints of Thinnfeldia odontopteroides'. the best fossils 

 were obtained at a well about 2 miles S.S.W. of Dubbo on the 

 Peak Hill road. Further down, about 5 or 6 miles S.S.W. of 

 Dubbo and about halfway between the Peak Hill and Obley 

 roads, I examined some hills locally known as the Gibraltar 

 Rocks. These consist of a grey, pepper-and-salt-coloured sanidine 

 trachyte containing magnetite, arfvedsonite, and segirine. It 

 intrudes Triassic sandstone and the adjoining quartz-porphyries. 



The occurrence of trachytes near Dubbo was first noted in 

 1905 by Mr. J. Murton, Geological Surveyor. Mr. W. S. Card 

 has kindly supplied me with a specimen of the arfvedsonite 

 trachyte found by Mr. Murton in the Parish of Dungarry near 

 Dubbo. Its chemical analysis (by Mr. B. White) is quoted in 

 my paper on the Warrumbungie Mountains. 



Mr. Staff-Surveyor Thomas, of Dubbo, informs me that there 

 are other knobs of trachyte at Minore, N.N. W. of Dubbo. Others 

 occur S.E. of the Gibraltar group; probably therefore there is a 

 string of these alkaline trachyte knobs connecting up the 

 Warrumbungles and the Canoblas. 



Mr. Card has lately received other interesting specimens from 

 Mr. Murton, including specimens of nepheline syenite, nepheline 

 phonolite.* 



The Barrigan mass of tinguaite, referred to in Carne's 'Mono- 

 graph on the Torbanite of New South Wales,' (Mem. Geol. Surv. 

 N.S.Wales)though of a similar age to the alkaline rocks abovedealt 

 with, does not lie on the same curve. The masses dealt with lie 



* "Miaskose,"see 'Petrological and MineralogicalNotes,'No.lO. Eecords 

 Geol. Surv. N. S.Wales, Vol.viii. 



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