304 GEOLOGY AND PETROLOGY OF THE GREAT SERPENTINE BELT OP N.S.W. 



western boundary of the mass is a strongly marked fault which crosses Werrie's 

 Creek obliquely. The eastern margin is a steep scarp. The andesite appears to 

 be cut off to the south by a dip-fault, and does not reach Back Creek. The thick- 

 ness of the sill does not apparently exceed three hundred feet at its eastern 

 margin . • * 



As in the case of the occurrences along the main zone of pyroxene andesite, 

 no exposures have been found of the contact between the igneous rock and tha 

 surrounding sediments^ and the classification of the four western masses as intru- 

 sive bodies again rests on their lithologieal resemblance to the rocks intrusive 

 into the Burindi beds two or three thousand feet lower in the stratigrapliical suc- 

 cession. Against this it might be urged that there is a lithologieal similarity no 

 less marked between the rocks of the main and western zone of pyroxene andesite 

 and those which in the Seaham and Clarencetown areas are considered to be 

 flows (4) . In our area the rocks are marked by concordant fluxional banding, and 

 by an absence of any evidence of a scoriaceous or spherulitie upper surface, or of 

 the presence of fragments of similar rock in the tuffaceous beds among which 

 they occur. These features, together with their gi-eat thickness and continuity, 

 are perhaps more in favour of an intrusive than an extrusive origin for the 

 andesite. 



Among the main minor sheets and sills, we may consider tliose of andesite, 

 quartz basalt and doleritc, and also those of keratophyre. 



A short distance below the Lower Glacial zone is a band of hornblende 

 andesite extending along the eastward slope of the ridge north of Cun'abubula, and 

 occurring again in a similar horizon in portion 88, near Proctor's, south of Curra- 

 bubula Creek. It is of the type of rock known as Martin's Creek andesite in the 

 Paterson region (4), weathers to an ochreous or buff colour, showing strongly- 

 marked fluidal structure, and in the rare fresh specimens is a grey-blue with 

 plentiful phenoerysts of plagioclase and hornblende. As before noted, the same 

 type of rock may be found in the Kuttung Rocks in Werris Creek Gap. The 

 rock of this type in the Paterson region is considered to be a flow : here it is classed 

 doubtfully as a sill. Decisive evidence is not yet available. 



Andesites and porphjrrites of several other types occur forming sheets in the 

 Warragundi hills. The (|uartz basalts are fine-grained, greenish-grey rocks which 

 are generally more or less vesicular. They occur in most noteworthy amount 

 forming two layers extending through the uppermost portion of the Kuttung 

 rocks from Werris Creek to within two miles of Currabubula. These are not 

 associated with basic tuffs, but seem to transgress the bedding planes of the sedi- 

 ments, and to be associated with dykes of the same composition. In the north- 

 west corner of the region mapjied, however, is an irregularly bo\inded layer of the 

 same rock, only about a yard in width where observed, intei-calated in ba,sic tutf. 

 This may perhaps be a flow. Some sheets of the same type of rock occur along 

 the eastern slopes of the Warragundi hills. Sills of dolerite occur in the Werrie 

 Volcanic Series, two very thick masses being known in, the hiUs east of WaiTa- 

 gundi Mountain, and thinner ones to the west, but these have not yet been 

 studied in detail . In the tuffs and conglomerates half a mile south-soiith-east of 

 Currabubula railway station, there is a sill whicli runs for about a quarter of a 

 mile, increasing in width until it is 120 feet across near the northern angle of 

 portions 271 and 287, where it is tnincated by a fault. Altlumgh of teschenitic 

 character and resembling some of the Tertiar\' intrusive masses, it is not neees- 



