BY W. N. BBNSON. 555 



north. They have here undergone considerable metamorphism, 

 which has increased their resistance to erosion, so that they form 

 a ridge between the granite and the valley of Seven Mile Creek. 

 Thus this arching of the strata is not a simple anticline, but an 

 ovoid pericline. The discontinuity of some of the beds suggests 

 that some faulting is also present, but this cannot be proved. 

 An apparent thickness of about a thousand feet of strata is ex- 

 posed below the limestone. 



Above the limestone are, here and there, masses of the fine- 

 grained quartzitic rock, and a thickness (at Tintinhull) of ap- 

 proximately four hundred feet of claystones with some radio- 

 larian limestones, and a small amount of pyroclastic material. 

 Elsewhere this zone is of greater thickness. The angle of dip at 

 times is quite small; one has been measured as low as 5° to the 

 S.S.W. Above these comes the great mass of pyroclastic rock, 

 which makes up the Igneous Zone. It is not more than one 

 hundred feet thick at the head of Loder's Gully, but increases in 

 width to the south, the outcrop being more than a quarter of a 

 mile across. The very indented outline of this mass is partly 

 the result of an interdigitation of claystones and tuflfs, but may 

 also indicate some repetition of beds by strike-faulting. The 

 wide zone of pyroclastic rock forms the crest of the ridge between 

 Loder's Gully and Seven Mile Creek, and, swinging round in 

 conformity with the limestone, and becoming more coarse in 

 grainsize as it turns, it is partly replaced by massive igneous 

 rock (porphyritic spilite) about half a mile south-west of Tintin- 

 hull railway-platform. The line of junction of the massive and 

 pyroclastic rock is not anywhere visible; indeed, there seems to 

 be a passage between the two. On either side of the massive 

 rocks is a varying amount of pyroclastic material, usually fine- 

 grained. It varies somewhat in character; sometimes it has a 

 granular base with a grainsize of about 0-5mm., but more usually 

 the base is aphanitic and more or less vesicular. Except for the 

 presence of vesicles, the rocks are very similar to those which 

 occur in the Eastern Series, in the Nundle district(l7, p. 146). 

 With these is a finegrained, apparently massive rock, which 

 microscopical study shows to be pyroclastic. The matrix of the 



