134 F. W. BUTTON. 



Tokatoka, Kaipara. — A grey, compact, sub- vitreous rock, with 

 small scattered hornblendes. S.G. 2-67. Section : Ground-mass 

 abundant, microlitic, the niicrolites -003 to -007 in length with 

 some magnetite grains. Probably there is no base, but a greenish- 

 brown decomposition product makes observation difficult. The 

 porphyritic minerals are plagioclase, hornblende, and magnetite. 

 There is a little secondary quartz. The felspars go to -04. The 

 hornblendes are brown, with a wreath of opacite, and up to "06 



AuctITE Andesite. 



ish-grey rock not shewing porphyritic 

 n : Ground-mass forming nearly the 

 ess glass usually longulitic but in 

 5 plagioclase microlites and laths up 

 to -02, and with scattered grains of magnetite and small patches 

 of chlorite. The porphyritic minerals are felspar and augite. 

 The felspar is allotriomorphic and up to -05 in diameter. The 

 augite is purple and slightly pleochroic, absorption y >- a or ^ ; it 

 goes up to -07 in length and is margined with grains of augite, 

 chlorite, and magnetite. Small black prisms, up to -015, scattered 

 through the ground-mass may be altered augites. From the quarry 

 at Logan's Point ; it is used for road-metal in Dunedin. 



Cave Valley, Oamaru. — A dark greenish-black compact rock. 

 S.G. 2-80. Section: Granular, composed of plagioclase, augite 

 and ilmenite in a small quantity of globulitic base. The plagioclase 

 is in laths about -01 in length. The augite is in grains from -OOl 

 to -002 in diameter and is distinctly gregaritic (Plate viii., fig. '<)* 

 the clusters going up to -04 in diameter, sometimes they enclose 

 the felspars and so become semi-ophitic. Occurs as a dyke in 

 diatomaceous ooze rock. Hutton, Trans N.Z. Inst., Vol. xix., 

 p. 419. 



Bank's Peninsula. — 1, A brownish-grey rock with large 

 yellowish-white felspars in groups. Section : Ground-mass 

 abundant, microlitic, chiefly felspar plates about -005 in diameter, 

 with a few laths and some grains of augite and of chlorite. The 

 porphyritic minerals are felspar and augite with some magnetite. 

 The felspar is chiefly well twinned plagioclase in square sections, 

 up to -16 in length, but there is also, perhaps, a little sanidine. 

 The augite is green and in small quantity, in crystals up to '02 in 

 length. There is also some chlorite after augite. Forms a dyke 

 on the top of the hills behind Opawa. Morten's Buildings m 

 Christchurch are built with it. 



2. A compact grey rock, the porphyritic minerals few and small- 

 S.G. 2-75. Section: Ground-mass very abundant, vitreous or 

 crystal litic, clear, with numerous microlites of felspar and augite- 

 The porphyritic minerals are plagioclase, augite, and apatite. The 



