340 GREAT S£Rf ENTINE BELT OF KKW SOtJTH WALES, vii., 



syncline. To the west of it there extends the broad, low, undu- 

 lating region composed chiefly of mudstones, extending to the 

 foothills of the ridges of Carboniferous rock that pass through 

 the Currabubula district. These are the mudstones of the 

 Burindi Series (on the extreme west), and the Barraba Series 

 which forms the greater portion of the Tamworth and Goonoo 

 Goonoo Plains. To the south-east, the tulf of the Pyramid Hill 

 Range apparently extends into the hills west of Nundle. 



The Stratiyraphical Position of the NiLudle Mudstones. 



The difficult question to be decided is the stratigraphical posi- 

 tion that must be assigned to the Pyramid Hill tuff. The syn- 

 clinal structure of the range, the lithological character of the 

 component rocks and the consequent topographic features, recall 

 the tuffs which form the hills west of the Tamworth Common. 

 These tuffs, etc., have been correlated with those occurring south 

 of the river in Portion 27, Calala(6, p. 580), and lie near, but not 

 on, the same line of strike as the Pyramid Hill tuff. The beds 

 which occur between the tuff of Portion 27, Calala, and the 

 nearest Loomberah limestone, are quite similar to those between 

 the Loomberah limestone and the Pyramid Hill tuffs, save for 

 the absence of the Scrub Mountain conglomerate. The first 

 impulse, therefore, would lead one to correlate the Pyramid Hill 

 tuff with the tuffs in the Tamworth Common, and, therefore, 

 with the Baldwin Agglomerate (6, p. 579). Such a correlation 

 would place all the mudstones of the Reedy Creek Valley, 

 together with the Nundle conglomerate, into the upper portion 

 of the Tamworth (Middle Devonian) Series, and would further 

 demand that none of the region mapped in the Nundle district 

 should belong to the Barraba Series, to which the western group 

 of mudstones (the Nundle Series) had previously been referred. 



But the study of the tuffs and breccias within the Devonian 

 Series shows that they do not always form on a single horizon, 

 but (what might have been anticipated) they formed at different 

 times, spreading out on either side of their centres of eruption, 

 and, therefore, lie at varying horizons. Apparently there were 

 epochs when eruption was more continuous and widespread than 



