BV W. N. BENSON^ W. S. DUN^ AND W. R. BROWNE. 303 



No indubitable evidence of the intrusive nature of this main zone of 

 pyroxene andesite has yet been found, and its classitieation rests chiefly on litho- 

 logical similarity with the rock of the eastern zone, and the similar absence of 

 characteristically volcanic features. The jaspery character of the brecciated rock 

 between the two overlapping portions of this zone, suggests that here is contact 

 metamorphism which has become most marked between the separated portions of a 

 split sill, but it is still possible that the apparent S]ilitting and shattering may be 

 due to a powerful strike-fault. 



The third zone is the most intermittent, thcnigh containing the broadest ex- 

 posures of pyroxene andesite. Of these the northernmost extends into the area 

 mapped from the Parish of Winton, crosses the upper portion of Chinaman's 

 Gully without producing marked relief, and becomes rather narrower until it is 

 fliaridy upthrown by a fault to form the shapely ridge of Duri Peak (Text-fig. 3). 

 In this the andesite is exposed as^a clift' of prismatic rock on the north-eastern 

 face, showing that the igneous stratum is about three hundred and fifty feet thick. 

 The south-western face is a dip slope inclined at an angle of 40° . The southern 

 flank of the mass is grooved by an L-shaped valley, the position of which was 

 apparently determined by a small strike fault intersecting a dip-fault, the latter 

 partly truncating the andesite, its plane being occupied by a basalt dyke. The 

 remnant of the andesite extending beyond this fault is cut off by a second one a 

 short distance to the south, which also displaced the main zone of andesite. 



The portion of the pyi-oxene andesite included between these two faults shows 

 most markedly a flow structure, especially on weathered surfaces, where the lines 

 of phenocrysts of plagioclase and pyroxene stand out distinctly from the glassy 

 matrix, which is often weathered to a bright red colour by the separation of dusty 

 haematite . 



About a mile to the south-east from here is a small mass of pitclistone (in 

 portion 116) from which was obtained the sample which has been analysed. It 

 forms an inconspicuous knoll. 



The pyroxene andesites appear again in the valley of Sandy Creek. Thev 

 are l)rought up to the surface by 9, fault (which has been traced westwards for 

 some distance), and thence the mass swells out to a width of about half a mile, 

 continuing for two miles to the south-east and rising to form a small group of 

 hills about five hundred feet above the floor of the valley. Two faults cross this 

 mass, displacing it slightly, and its southern margin is also a fault traceable tor 

 some distance westward. An interesting feature of this mass is its three-fold 

 nature. The highest hill is seen to be craggy on the easterly and westerly 

 aspects, the rock composing the slopes being very glassy, but in the centre of the 

 hill there is a smooth saddle, slightly lower than the sides, and composed of 

 lithoidal andesite. Possibly the mass is twofold in nature, the vitrophyric ex- 

 ternal segments having a lithoidal inner portion. In other parts of this 

 region is seen a close association of lithoidal and glassy rocks uf otherwise simi- 

 lar nature, and forming part of a simple mass. The significance of this will be a 

 matter of interesting research. A somewhat analogous association has been 

 found to be not uncommon in Western Scotland (24). This ma.ss, if stratiform, 

 must be nearly fifteen hundred feet thick. 



The last occurrence of pyroxene andesite remaining for description is that 

 which forms Kingsmill's Peak at the head of Curiabubula, Werrie's and Back 

 Creeks. In this mass the width of the exposed surface of pyi-oxene andesite is 

 gi-eater than elsewhere owing to the smaller inclination of the dip-slope. The 



