BY W. N. BENSON. 581 



3. The Nundle Series is quite analogous to the Barraba mud- 

 stones, with which they are correlated. It lies on the Bowling Alley 

 Series, and in absolute conformity with it. It is very difficult 

 indeed to draw any precise line of division, the formations shading 

 one into the other. The lithological change lies in the replacement 

 of the cherty claystone by a finely laminated, green-brown mud- 

 stone, with thin layers of yellowish felspathic material, which 

 becomes the dominant rock of the formation. The igneous activity 

 diminished, and is expressed by thick layers of a fine, even-grained 

 tuff of the same mineral composition as the ground-mass of the 

 coarse breccia, but is almost free from cherty fragments. Large 

 and small lenses of blue, argillaceous, non-fossiliferous limestone 

 are frequent. Here and there, conglomerate bands are present, 

 and one well-marked zone can be traced from west of Yellow Rock 

 Hill, across Nundle Sugarloaf (in front of Square Top), and 

 north-west to Rodney Mountain, west of Bowling Point, beyond 

 the limits of the map. The finer mudstones, in this series, contain 

 radiolaria, and Lepidodendron australe is also present. 



These beds dip to the south of west at angles gradually decreas- 

 ing as one goes westward, though increasing again after some dis- 

 tance. Their thickness, measured along Jimmie's Creek to the 

 summit of Square Top, is apparently 13,000 feet, but probably 

 there is much repetition. The fault shown near Nundle, displacing 

 the base of this formation, cannot be taken as proved, but is merely 

 offered as a suggestion to account for the facts observed there. 



4. The Dolerite. — This rock is present in very great amount, 

 and its distribution calls for comment. It is chiefly in the Lower 

 Radiolarian Claystones and Breccia, and the Upper Claystones, but 

 is present, to only a very small extent, in the Upper Breccias. As 

 far as the mapping goes, it appears to form large, irregular, sill- 

 like intrusions, and has been traced throughout the series, from 

 Hanging Rock to Black Jack. Time has not permitted their being 

 mapped north of Hyde's Creek, though they are less common than 

 to the south. They have been much disturbed; mining operations 

 at the foot of Hanging Rock, and elsewhere, have shown that the 

 country is full of "slides." Occasionally, as at Bowling Alley 



