262 PROCEEDINGS OF SECTION C. 



greenish-grey rock, fifteen feet thick at the base, sharply defined 

 on the western side — the line of division dipping 55° West, — but 

 on the eastern side passing insensibly into the soft decomposed 

 rock. It is an enstatite andesite with a small amount of devi- 

 tritied ground-mass. The crystals are plagioclase (much decom- 

 posed), bastite, chlorite pseudomorphous after augite, and titani- 

 ferous magnetite in large grains, changing into leucoxene. It 

 has been supposed that this mass cannot be part of a dyke 

 because it passes insensibly into soft rock ; but there is no reason 

 why a dyke should not decompose, and its almost holocrystalline 

 texture as well as the large grains of magnetite in the ground- 

 mass seem to me to be decisive against its being a lava stream, 

 S.G. = 2.716. 



3. — In Collarbone Creek a hard dyke-like mass occurs a little 

 above its juncture with the Karaka. The rock is an enstatite 

 andesite of a greenish-black colour and highly charged with 

 pyrites. The ground-mass is fairly abundant, colourless, with 

 large magnetic grains and felspar microlites. The crystals are plagio- 

 clase, averaging 0.024 in length, sometimes infiltrated with chlorite, 

 and pyroxene in stellate groups often 0.05 inch in diameter, 

 some of which arealtered to chlorite or bastite. S.G. = 2.767. 



4. — When walking up the bed of the Karaka Creek the first 

 hard rock observed is a dyke-like mass crossing the creek and 

 forming a small waterfall. It is a hornblende andesite very 

 compact and of a dark grey colour. The ground-mass is abundant, 

 pale in colour and contains rather large grains of magnetite. The 

 felspars and hornblends are all decomposed, the latter into a 

 colourless black-bordered aggregate, with occasionally a little 

 chlorite ; there is also some bastite. The minute texture of this 

 rock is not so chracteinstically dyke-like as any pi the foregoing, 

 but, as it differs mineralogically from the surrounding rocks, it 

 will probably prove to be a dyke. S.G. = 2.665. 



5. — The hornblende dacites from the Waiotahi were originally 

 described by me as dykes. The place where I obsei"ved them is now 

 covered up, but a microscopic examination of specimens confirms 

 my opinion that they come from dykes, because they have a 

 distinctly ophitic structure, and large grains of magnetite in the 

 base. 



6. — I have also enstatite andesites from boulders in the 

 Waiotahi and Karaka both of which, I have no doubt, came from 

 dykes. Both have large magnetite grains in the ground-mass and 

 both shew intergrowths of rhombic and monoclinic pyroxene. 



Looking over the whole of my specimens I should judge that 

 of the three hornblende dacites, two are from dykes, the third 

 from a lava stream. The enstatite dacite is a lava. All the five 

 hornblende andesites appear to be from dykes. Of the fourteen 

 augite andesites a large majority are lava streams ; and of the 



