228 OREAT SERPENTINE-BELT OF NEW SOUTH WALES, vi., 



Carbuiiifei'ous Coal-Measures, which rest uiiconfoiinably on the 

 Rocky Creek conglomerates. Jurassic(?) sandstones overlie these, 

 and extend over the DeNonian formations: and Tertiary gravels, 

 clays, and diatomaceous earth follow, together with a complex 

 series of alkaline lavas in the Nandewar Mountains, and much 

 basalt, both there and elsewhere. 



With the exception of the Baldwin Agglomerates, and the 

 dulerite-sills of the Barraba mudstones, all these formations have 

 been noted by earlier writers; but their distribution, and strati- 

 grajDhical relationships, and the tectonics of the district, were 

 imjDerfectly known. 



Regional GeolocxY. 

 In our discussion of the regional geology, it will be most con- 

 venient to divide the area into a series of zones, each of which is 

 characterised by a fairly uniform tectonic structure. These are : 

 (i.)the Eastern Zone, consisting of the marginal portion of the New 

 England granites, and the highly disturbed complex east of the 

 .Serpentine Line; (ii.) the Serpentine Line; (iii.) the Near Western 

 Zone, consisting chiefly of isoclinally folded Tamworth, Barraba, 

 and Burindi rocks adjacent to the Serpentine Line; (iv.) the 

 Middle AVestern Zone, chiefly consisting of a broken anticline of 

 Baldwin Agglomerate and Barraba mudstone ; (v.) the Far 

 AV^estern Zone, an undulatory but chiefly westerly dipping series 

 of Barraba, Burindi, and Rocky Creek rocks; and (vi.) the Nan- 

 dewar Mountains, consisting of Tertiary volcanic rocks. The 

 distincti(Hi must be clearly made between the Nandewar Mount- 

 ains and the Nandewar Range, which is merely the ridge 

 between the Gwydir and Namoi River watersheds. 



i. The Eastern Zone. 

 AVe commence the description in the south. The Namoi 

 River is conflned to a gorge by a ridge of red jasper jDassing into 

 jasperised slates and ferruginous phyllites, immediately west of 

 the Serpentine Line, which crosses the river about fourteen 

 miles above Manilla. Dykes of lamprophyre intersect this ridge 

 (1, Ft. iii., p.698). East of the ridge, which is two miles wide, 



