GEOLOGY OF ERUPTIVE AND ASSOCIATED ROCKS, POKOLBIN. 379 



The GEOLOGY of the ERUPTIVE and ASSOCIATED 

 ROOKS OF POKOLBIN, NEW SOUTH WALES. 



By W. R. Browne, b.sc, and A. B. Walkom, b.sc, 

 Demonstrators in Geology, University of Sydney. 



With Plates XXV -XXVIII. 



[Read before the Royal Society of N. 8. Wales, December 6, 1911.] 



I. Introductory. 

 II. Physiography and Preliminary. 



III. Faults. 



IV. Geological Age of the Formations. 

 V. Geology — A. Carboniferous Rocks. 



Drake's Hill Area. 

 Mount Bright Area. 

 Matthews' Gap Area. 

 B. Permo-Carboniferous Rocks. 

 VI. Order of Succession. 

 VII. Petrology. 

 VIII. Summary. 

 IX. Conclusion. 



Introductory. 



The district which it is proposed to deal with in this 

 paper is situated in the County of Northumberland, about 

 six miles from the town of Cessnock. The eruptive rocks 

 lie in the Parishes of Rothbury, Pokolbin and Milfield, and 

 comprise an area about six miles long by about two miles 

 broad at the widest part, the longer axis being roughly 

 north and south. 



So far as we are aware, no detailed description of the 

 igneous rocks of this district has hitherto been published. 

 In Professor David's "Geology of the Hunter River Goal- 



