114 E. 0. Teale: 



Creek reveal tlie existence of bands of altered andesitic and' 

 trachytic rocks. 



Ihe fragmental character of much of the rock is frequently 

 apparent macroscopic ally, and thin sections shoAv clearly that much 

 of the finer material too, though often much altered and silicified, is 

 of a pyroclastic origin. 



An alternation of coarse and finer-grained material, with slight 

 indication of bedding, appears to be the general rule, definitely 

 stratified beds being rare. HoAvitt (3) observes that he had only 

 noted at one place, near Buchan, a section which suggested aqueous 

 assortment and deposition, which he regarded as of limited extent 

 and purely local. Though this appears to be true in the main, in the 

 area under consideration, the outcrops in the southern extremity 

 afford an exception, for at Section A, Boggy Ci-eek, and Section D, 

 Ironstone Creek, particularly, the character and rejrularity of the 

 bedding are such as to strongly suggest aqueous deposition. In this 

 region also t)vo other exceptional features are worthy of note : the 

 beds are highly inclined, and intensely sheared, the latter agency 

 having converted the rocks into typical porphyroids. These are best 

 developed at Section E, Nowa Nowa railway bridjre- The schistose 

 character is marked along the Boggy Creek Gorge for nearly a mile 

 above the railway bridge, but gradually disappears beyond this. 

 The direction of schistosity corresponds with that of the strike of 

 the different beds, being in a general N. to N.N.E. direction. As 

 the course of the stream bed ii here about N.W., it is a favourable 

 one for exposing a good line of Section. For general and petrologi- 

 cal description, it wil be convenient to group the rocks as follow : — 



(a) Porphyroids. 



(b) Stratified ash beds. 



(c) I'rachytic and andesitic rocks. 



(d) Acid porphyritic and pyroclastic rocks. 



(e) Ceratophyres. 



(f) Granitic rocks. 



The Porphyroids. — Ihese rocks form a rather striking group, 

 for their schistose structure, and often also a sheen or lustre due 

 the development of sericite give them a distinct lithological 

 character. Their junction with the underlying sediments, presum- 

 ably Upper Ordovician in age (Section E, Boggy Creek), is sharp 

 and unconformable. They are again exposed in the bed of Iron- 

 stone Creek (18-22), and still .further to the N.E. towards the head 

 of one of the branches of Bill's Creek (below No. 68"). 



* 



