simultaneously, or in square sections which extinguish at angles 

 up to 8° with the cleavage. The augite is dark green and up to 

 •02 in length. From a dyke on the bridle track between Heath- 

 cote and Lyttelton on the Lyttelton side. I doubt its being a 

 true trachyte, but it is probably the same rock as that which Dr. 

 Kolenko has described as a trachyte from the tunnel in which the 

 ground-mass is composed of nearly equal parts of felspar microlites 

 and augite prisms. (N.Z. Journal of Science, Vol. ii., p. 552). In 

 my specimen the augite of the ground-mass is quite subordinate 

 to the felspar. 



3 Pale grey rocks with scattered black augites and a few felspars 

 Section : Ground-mass very abundant, microlitic, formed of felspar 

 microlites, -005 in length, and augite prisms, -001 to -002 in length, 

 ■with some magnetite dust ; the augite quite subordinate to the 

 felspar. The porphyritic minerals are sanidine, plagioclase and 

 augite. The plagioclase is well twinned, the sanidine in binary 

 twins up to -08 in length, The augite is pale green, rare, up to 

 •02 in length. There is sometimes a little chlorite. Forms dykes 

 on the road between Heathcote and Sumner. The sanidine is 

 doubtfully identified. 



Enstatite Trachyte. 

 Runanga, E. Taupo Co. — A pale grey rock with abundance of 

 1»ro\vu spots of enstatite surrounded by a wreath of iron oxide, 

 •"id of colourless felspars. Fracture earthy. Section : Ground- 

 mass very abundant, colourless, crystallitic, longulitic, with 

 scattered felspar microlites -004 in length, shewing fluxion. The 

 porphyritic minerals are sanidine and plagioclase in about equal 

 quantity, enstatite and small quantities of augite and hornblende, 

 with magnetite in crystals and grains. The felspar crystals are 

 about 04 in length. The enstatite is in prisms, -03 in length ; 

 pleochroic, a and ft pale yellowish-brown, y pale bluish-green. The 

 augite is pale green and the hornblende brown. Both are in small 

 f^ystals not more than -02 in length. This rock covers a consider- 

 "'ie area between Runanga and Tarawera on the Napier Road. 

 '"1-, Rep. Geol. Expl. 1870-1, p. 160. 



Division II.— PLAGIOCLASE ROCKS. 



• -ioclase (excluding microcline) is always present, orthoclase 



- '"sent or rare. Hornblende or augite, or both, generally ac- 



'i"l»'iiiy the plagioclase. Biotite, enstatite, or olivine may or may 



iiot he present. The soda exceeds the potash. 



LIME-SODA SERIES. 



■^iliea 65 to 55 per cent. Iron oxides 6 to 13 per cent. The 



■ md magnesia together are more than the alkalies. The lime 



i^ less than one-half of the alumina and more than the soda. 



