168 THE GKOLOGY OF THE CANOBOLAS MOUNTAIN'S, 



On the Pininacle RoArl, about 1} miles froQi the suininit of The 

 Pinnacle, tuffs occur, containing ejected blocks ranging up to 

 1 ton, or even more, in weight. A somewhat similar outcrop 

 occurs at Norris's Farm, on the western side of the Canobolas. 

 All these tuffs are essentially trachytic in composition, but con- 

 tain numerous fragments of the earlier and more acid comendites, 

 etc. The tuff-beds, as far as could be observed, dip away from 

 the central area. They also outcrop on the road leading to the 

 top of the Old Man, but this, and several other small outcrops, 

 have not been shown on the accompanying map. Mr. T. Harvey 

 Johnston, B.Sc, informs us that he found fragments of coniferous 

 wood in these tuffs near German's Hill. 



(c) The Andesites. — These lavas are of a somewhat basic type, 

 and contain numerous pheuocrysts of plagioclase, with occasional 

 phenocrysts of augite and olivine. They are sometimes vesicular. 

 A reference to the map will show that they are extensively 

 developed to the west and north of the area dealt with. The 

 boundaries shown on the map are onh' approximate; firstly, because 

 the area to the west and north-west was not surveyed in detail; 

 and secondly, owing to the frequent difficulty in discriminating 

 between the decomposed outcrops of the more basic trachytes and 

 andesites respectively. 



The Old Man Canobolas was the point of eruption from which 

 these lavas were derived. Prof. David, in the note alread}' 

 referred to, gives the following description of the neck or plug on top 

 of this mountain : — " At a point bearing S. 15° W., 78 yards dis- 

 tant from the Trigonometrical Station on top of the ' Old Man 

 Canobla ' is, what the author considers to be. the central ' neck ' 

 of the volcano, in the shape of a nearly circular mass of coarsely 

 crystalline very dense andesitic lava, rising from four to five feet 

 above the general level, and showing stronglj'- marked oblique 

 lamination, the laminie dipping in towards the centre of the neck 

 at an angle of from 40° to 60°. The neck is about J chain in 

 diameter, and is surrounded by beds of scoriaceous lava to the 

 north and scoria to the south. The beds of the former to the 

 north dip nortlierl}" at about 15°, and are overlaid by a dense 



