380 W. R. BROWNE AND A. B. WALKOM. 



field of N.S.W.," Part I, 1 there are allusions to Pokolbin, 

 and the eruptive complex is referred to as a Carboniferous 

 inlier. A sketch map is given, and some sections indicate 

 suggested relationships between the rocks, which are 

 referred mainly to Carboniferous times, with some con- 

 temporaneous lava flows in the Lower Marine of the Permo- 

 Carboniferous. This is, to the best of our knowledge, the 

 only place in geological literature where reference is made 

 to the igneous rocks of Pokolbin. We propose to treat the 

 district in some geological detail, since, though it is of no 

 very great extent, it possesses a very interesting geological 

 history. 



For convenience of treatment and reference the district 

 will be divided into three areas : — 



(i) The Drake's Hill area, extending from a point about 

 half a mile north of the southern boundary of the 

 Parish of Rothbury to "Maluna" homestead. 



(ii) The Matthews' Gap area, from Maluna to Mat- 

 thews' Gap. 



(iii) The Mount Bright area, from Matthews' Gap as 

 far south as the "Jerusalem Rock" and Mount 

 View School, including the northern portion of 

 Mount Bright. 



These areas are by no means to be separated geologically 

 or petrographically, as we shall endeavour to show that 

 the rocks of the whole district, with a few exceptions, are 

 to be considered as forming part or all of a geological unit. 



Physiography and Preliminary. 



The northern portion of the district forms a chain of 

 foothills to the Brokenback Range, whose steep scarp runs 

 in a general E.S.E. direction as far as Matthews' Gap, 

 where it takes a sudden turn to the east. Continuing thus 



1 Memoirs of Geol. Surv. N.S.W., Geology No. 4, 1907. 



