BY W. N. BENSON. 251 



ing disturbance and development of easterly dipping, isoclinal 

 folding, from the Manilla River to the Carboniferous rocks of 

 the zone last described. They are interbedded with cherty 

 radiolarian bands (as at Black Springs), and with thick zones of 

 fine breccia and tuff which form prominent ridges, such as the 

 Aberdeen and Thunderbolt's Gap Ranges, or with coarse angular 

 breccias, such as those at the Rocks Crossing of the Manilla 

 River on the Barraba-Crow-Mountain Road. Between these 

 resistant zones, the Manilla River winds back and forth as it 

 crosses them obliquely. Between the Aberdeen and Thunder- 

 bolt's Gap Ranges is a patch of Tertiary drift about 80 feet 

 thick, capped by basalt 160 feet thick, which extends for a mile 

 in a S.S.E. direction. It was described by Mr. Pittman(9). See 

 also p.277). 



We return to Manilla — West of the river, the Baldwin 

 Agglomerate, dipping to the east, rises to form the Baldwin 

 Range, which is cut off by a series of faults which throw-down 

 to the west. The same feature occurs again in the Black 

 Mountain region, and there can be little doubt that the great 

 group of roughly meridional faults extends far to the north and 

 to the south of this mountain-group, but their effect is not 

 rendered obvious owing to the soft, non-resistant character of the 

 Barraba Shales. The structure of the Baldwin and Black 

 Mountain Ranges is, however, rendered very clear by the great 

 resistance offered by the Baldwin Agglomerate, and the compara- 

 tive non-resistance of the overlying mudstone. Except where 

 they are trenched by canyons, as in Borah Creek Gap, the 

 surface of the Baldwin Agglomerates has been merely laid bare 

 by the removal of the Barraba Mudstone; and the various faults, 

 which cut up this region into a series of strips, are rendered 

 quite obvious. This can be proved by following the course of 

 Borah Creek along the Section line CBA. (See Section 1, PI. xx.). 



On the steep westerly slope of the Baldwin Range, excellent 

 exposures of agglomerate are to be obtained, a thickness of 1,600 

 feet being measured. The rock is very like the agglomerates at 

 Tamworth. (See 1 Pt. i., p.500: also Pt. v., pp.577-8). Irregular 



