438 Transactions. — Geology. 



greenish-grey rock crowded with crystals of feldspar and 

 hornblende just discernible to the unaided eye, and imparting 

 a rough impression to the touch. Base clear ; not abundant, 

 but, like No. 3 dyke, crowded with microlites and crystals of 

 feldspar and hornblende. Feldspars fresh, but often clouded 

 with inclusions ; zonally arranged. Not much twinned. 

 Hornblendes generally altered. Calcite and secondary quartz 

 present. Iron not abundant, except as fine dust in base and 

 around hornblendes. 



Dyke No. 5. — This begins about 400 yards further south. 

 It trends east and west, and shows a width of about 125 ft. 

 This rock is much altered. Colour on surface pale bluish- 

 grey sj)eckled with chlorite, imparting porphyritic appear- 

 ance. Ground-mass clear. In polarised light presents a 

 finely granular appearance, due to presence of grey microlites 

 of fairly uniform size. 



Feldspar phenocrysts not numerous ; mostly fresh, and 

 not much twinned. Slides contain isolated crowded aggre- 

 gates of small plagioclase crystals, not much twinned, but 

 fresh, and showing bright polarisation colours. The horn- 

 blendes are mostly altered to chlorite or replaced by mag- 

 netite. All are bordered with magnetite. 



Dyke No. 6. — This occurs 330 yards south of No. 5. It 

 has an exposure about 400 yards long. A very dense black- 

 ish-green rock, with conspicuous crystals of feldspar. When 

 wet almost dense black. Ground-mass abundant, dark 

 bluish-grey, in places almost black, from presence of clouds 

 of iron-dust. Feldspars plagioclase, not abundant ; occur 

 only as large idiomorphic plates, not much twinned; fairly 

 fresh and clear. The hornblendes are completely altered to 

 serpentinous matter. Their original crystalline forms are 

 sharply outlined by narrow, but very even, distinct black 

 borders of magnetite. Parts of interior often occupied by 

 clear matter. A little calcite and haematite are present. 



Dyke No. 7. — This begins about 300 yards further south, 

 and thence extends to Mata Stream. It is a greenish-grey 

 rock, much decomposed near the surface; feels rough to 

 touch ; shows crystals of feldspar and hornblende, imparting 

 a granular appearance to rock. Base clear, but not abund- 

 ant ; crowded with microlites and plates of feldspar and 

 hornblende. Feldspars fresh, but not very clear, from pre- 

 sence of inclusions ; mostly well-twinned plagioclase. Extinc- 

 tion angles indicate basic variety. A little sanidine present. 



Hornblende occurs both fresh and changed to chlorite 

 and serpentinous matter ; some plates show black resorption 

 borders. Apatite present ; iron fairly abundant. 



In a paper read before the Australasian Association for the 

 Advancement of Science Captain Hutton, F.B.S., describes a 



