BY W. N. BENSON. 273 



high plateaux of southern New England. These two portions 

 of the western boundary of New England are structurally 

 collinear, but instead of the boundary of the highland continuing 

 the line between these two segments, there extends at right 

 angles thereto the Nandewar Range terminating in the Nande- 

 war Mountains, beyond which the surface-level sinks rapidly to 

 the western plains near Narrabri. Further, the height of the 

 Nandewar Range increases from Barraba to the west, and other 

 evidence (to be detailed later) supports the view that the region, 

 which protrudes to the west of the normal western boundary 

 line of New England, has been uplifted in the Nandewar 

 Mountains, and tilted against the flanks of the New England 

 plateaux. Its western limit, according to Dr. Jensen's observa- 

 tions, must be a series of flexures or faults (See Text-fig.l, p.229). 

 To the south-west and north-west, it seems to have warped down 

 into the plain. At or near the most elevated portion of the edge 

 of this easterly tilted region, lie the Nandewar Mountains, a 

 fact which suggests that the elevation and volcanic activity were 

 genetically related processes. A further feature, probably due 

 to crust-movement, is to be found south-east of Bingara, where, 

 stretching south of the Gwydir River, is a widely extending 

 region of lowland, which is believed to be a senkungsfeld-region. 

 This will be discussed further below (p. 280). It is chiefly 

 occupied by Mr. Munro's station, Keera. 



ii. Features due to Volcauic Eruptio7is. — Two main groups of 

 features are due to volcanic eruption, namely, (a) the great dis- 

 sected pile of the Nandewar Mountains, and (6) the basalt-flows 

 which descended the ancient rivers, covering their drift-beds 

 (often of considerable thickness). Of these, the trachytes are 

 probably the older, but it is not certain that all the basalts are 

 even approximately coeval. Two flows certainly occurred near 

 Bingara, separated by 120 feet of gravel, but their outpourings 

 are considered to have been separated by a very short period of 

 time (19). Two important regions of basaltic rocks remain un- 

 mapped, namely, that in the Keera Senkungsfeld, and that near 

 Myall Creek. Until these are studied, the Tertiary history of 

 the region will be indefinite. 



