GEOLOGY OF THE GLOUCESTER DISTRICT, N.S.W. 239 



Tlie width of the outcrop, taken in conjunction with the 

 dip of these spillites in the Bundook neighbourhood, would 

 give a thickness of several thousands of feet for these rocks. 

 Quite probably some strike faulting has taken place, giving 

 duplication of outcrop. Even after allowing for this possi- 

 bility, their actual thickness must be at least 2,000 to 3,000 

 feet. Such a great thickness of spillite ("pillow") lavas 

 has not, so far as the writer is aware, been recorded from 

 any other locality; and it at once raises the question as 

 to whether the conditions of deposition usually postulated 

 for such rocks are correct. 



(b) The Tuffs, — These have a very large development, 

 and are interstratified everywhere throughout this district 

 with the other Devonian sedimentary rocks. They are 

 typically fine-grained in texture, with a greyish-blue colour, 

 and intermediate to subacidic in composition. Both coarser 

 and darker coloured varieties also occur. These tuffs are 

 in general regularly interstratified with the other sedi- 

 mentary strata, but in many places they are seen to have 

 intrusive relations with the radiolarian cherts and clay- 

 stones, similar in every way to the intrusive tuffs of 

 the Tamworth District described by Messrs. David and 

 Pittman. 1 Particularly fine examples of these intrusive 

 tuffs can be be obtained from the spoil heaps at the Moun- 

 tain Maid Mine at Oopeland, and excellent examples may 

 also be seen in the railway cuttings between Gloucester and 

 Bundook. The individual layers of tuff vary much in 

 thickness, ranging from less than one inch to upwards of 

 100 feet in thickness. No really satisfactory explanation 

 of these anomalous "intrusive tuffs" has yet been put 

 forward. 



(c) The Radiolarian Cherts and Clay stones. — These con- 

 stitute the most abundant of the strata of the Tamworth 



1 "On the Paleeozoic Radiolarian Rocks of N.S. Wales, Q.J.G.S., 1899, 

 pp. 16 - 37. 



