20 E. Wynne Hughes — Geology of 



at the north-east end of the hill, quite a number of pebbles of 

 rhyolite, some 3 to 4 inches long, are seen, but the majority of the 

 pebbles are small and well rounded. It is only in this exposure 

 that we get any indication of stratification in the conglomerate. 

 Generally the dip of the rock is quite obscure, as is often the case in 

 massive conglomerates ; but in the freshly cut rock in this quarry 

 alternate layers of pebbles and fine grit are distinctly visible. The 

 lie of the pebbles suggests a dip of about 50° to S.E. In the quarry 

 the rock is seen to be jointed, some joints sloping in the direction of 

 the dip of the pebbles, crossed by others at right angles. 



(b) Microscopic Examination. — Several thin sections were prepared 

 from specimens collected from different places along the outcrop, 

 both from the highly pebbly conglomeratic portion and from the less 

 pebbly and more gritty portion. Every slide confirms the con- 

 glomeratic nature of the rock. They show the presence of felspar, 

 quartz, and numerous chips of rhyolite and fragments of tuff 

 (PI. I, Fig. 6 ; PL II, Fig. 1 ). The felspars usually exhibit multiple 

 twinning, but are mostly decomposed. The quartz almost 

 invariably show subangular edges. The matrix is felspathic and 

 fine-grained, often containing small crystals of muscovite. 



Sections of some of the larger pebbles were also examined, and 

 these compare in every respect with the rhyolitic rocks described 

 above (p. 19). They contain crystals of felspar and quartz embedded 

 in a felsitic groundmass, which in some cases shows a characteristic 

 flow-structure. 



At right angles to the strike — in a south-east direction — the 

 conglomerate rapidly changes to a grit, the width of a distinctive 

 conglomerate being about 18 feet. 



(ii) The Grit Band. — (a) This band of grit is about 12 feet thick, 

 and extends from the south-west to the north-east end of the hill. 

 Under the microscope the grit is seen to contain angular and sub- 

 angular crystals of quartz in large number, along with numerous 

 felspar crystals (partly kaolinized) ; and occasional chips of rhyolite 

 also occur (PI. II, Fig. 1). 



(b) This fine grit, when followed southwards across the strike, 

 gives place to a distinctly coarser rock which is very much weathered. 

 When followed along the strike to the south-west this rock becomes 

 still coarser and still more weathered. A. microscopic examination 

 shows the rock to be largely composed of angular quartz crystals — 

 often sheared — set in a felspathic cement (PI. II, Fig. 5). 



Both these bands of grit, fine and coarse, persist in a north- 

 easterly direction for a distance of 900 yards, with but a slight break 

 where the hill is capped with drift. At the north-east end of the 

 hill there is the same succession of conglomerate, fine grit and coarse 

 grit, precisely as one would expect to find them on the supposition 

 that the dip is, as stated above, S. 30° E. 



There is a decided dip in the ground beyond the outcrop of the 

 quartz grit, and no further exposure is visible, all the land on the 

 south-east side of the grit being under cultivation. This is most 

 unfortunate, as it is impossible without further exposures on that 

 side to determine the exact relation of the grits to the other 

 formations of the district. 



