405 



THE GEOLOGY AND PETROLOGY OF THE GREAT SERPENTINE 

 BELT OF NEW SOUTH WALES. 



Part IX. — The Geology, Palaeontology and Petrography of the 



CURRABUBULA DISTRICT, WITH NOTES ON ADJACENT REGIONS. 



By Professor W. N. Benson, B.A., D.Sc, F.G.S., W. S. Dun, and 

 W. R. Browne, B.Sc. 



Section C. — Petrography. 



By W. R. Browne, B.Sc, Lecturer and Demonstrator in Geology, 

 The University of Sydney. 



(Plate XXV.) 



Page. 



Introduction 405 



Extrusive Rocks 406 



Intrusive Rouks ■ • 410 



General Remarks 421 



Comparison with other Carboniferous Areas in the State .. .. 422 



Introduction. 



The igne<ius rocks ot the Currabubula district are of interest, both on account 

 of the variety in type and in mode of occurrence which they present, and because 

 of the striking resemblance which many of them bear to the volcanic rocks of 

 Carboniferous age in other parts of the State, and particularly to the extensive 

 series which form so important a part of the Carboniferous area at Clarencetown, 

 Paterson. Seaham and elsewhere in tlie Hunter River basin, about 100 miles away 

 to the S.S.E. of Currabubula. 



Igneous activity appears to have l)egun in this area during the Burindi epocli, 

 and was confined, so far as is at present known, to explosive outbursts : no out- 

 crops of massive volcanic rock have been found, but fine-grained tuffs occur at tlie 

 top of the Burindi Beds. The display of igneous activity, however, culminated 

 during the laying down of the Kuttung Series and continued apparently right 

 to the close of the Carboniferous period. 



The chronological sequence of the igneous rocks can never be determined with 

 the same accuracy and definiteness with which it can be established in the more 

 southern areas, for the reason that the series is partly extrusive and partly in- 

 trusive, and so mutual relationships can often not be observed. This must also 

 render tlie precise stratigrapliical position of some of the rocks a matter of un- 

 certainty : for example, the great series of pyroxene andesite sills, whicli are so 

 important both physiographically and petrologically in the area, have been found 

 intrusive only into the Burindi Beds and the overlying "gi-its," so that their exact 

 time-relations to the conglomerates and glacial beds of the Kuttung Series cannot 



