Vol. 70.] LAVAS AT THE XORTH HEAT), OTAGO HABBOL'B. 389 



(21) Trachydolerite (called 'basanite' by me in 1906). — 

 Large phenocrysts of nepbeline and of sodalite are fairly abundant, 

 and the rock thus has a coarse porphyritic habit. These crystals 

 are surrounded by a zone of secondary minerals, chiefly calcite and 

 natrolite. Small crystals of segirine measuring in longest diameter 

 •3 mm. Some grains of olivine, '7 mm. in diameter, altered into 

 serpentine and calcite. 



Ground-mass very fine-grained. Microlites of aeffirine-aueite form 

 the most striking constituent. They contain grains of magnetite, 

 and in many instances when they are irregular in shape they have 

 been clearly derived from the resorption of hornblende. The clear 

 mineral has no definite form, and is for the most part nepheline, 

 though a few microlites of felspar can be distinguished. A con- 

 siderable quantity of magnetite occurs in minute grains. Occasional 

 crystals of brown apatite. Xepheline 40 per cent. ; felspar 16 per 

 cent. ; segirine-augite 37 per cent. ; magnetite 7 per cent. 



(20) Basalt. — Labradorite -phenocrysts fairly abundant. 2 x '7 

 mm. ; augite brown and slightly pleochroic, 5 x 3 mm. ; a few 

 rounded olivines, "5 mm. 



•Ground-mass: indistinct flow-structure ; labradorite, T5 X "03 mm.. 

 62 per cent. ; pale-green augite, '02 x '00-3 mm., 31 per cent. ; 

 magnetite, "01 mm., 7 per cent. 



(19) Basalt. — Small glomeroporphyritic patch of felspar and 

 greenish augite, but no true phenocrysts. 



Ground-mass: labradorite-laths. 3 X '03 mm., -35 per cent.; 

 augite, "8 X 03 mm., 4-3 per cent. ; magnetite, "04 mm., 10 per cent. ; 

 a very few small olivines. 



(18) Basalt. — Large patch of labradorite-crvstals, -3 mm. ; also 

 single crystals, 1*5 X "5 mm. One large crystal of anorthoclase, 

 2 *5 mm. ; pale brownish- green augite, twinned, not pleochroic, 

 T X 05 mm. ; olivine, 1 X '05 mm. 



Ground-mass : labradorite, "08 X '02 mm., 67 per cent. ; pale- 

 green augite-microlites, '05 X '02mm., 19 percent. ; olivine rounded. 

 '05 mm.. 4 per cent. ; magnetite '02 mm., 10 per cent. 



(17) Basalt. — Glomeroporphyritic aggregates of acid labra- 

 dorite, 6 mm. Corroded crystals of anorthoclase, 2 x '3 mm. 

 Brownish-green pleochroic augite. poorly zoned : includes small 

 pieces of olivine, sometimes twinned. Olivine small, infrequent. 



Ground-mass : acid labradorite, '08 X '02 mm., 70 percent. ; pale- 

 green augite-microlites, '05 X '02 mm., 16 per cent. ; olivine, "03 mm., 

 4 per cent. ; magnetite. '02 mm., 10 per cent. 



(16) Basalt. — Phenocrysts of labradorite, 3'5 x 1 '5 mm., con- 

 taining many inclusions of magnetite and of augite, in which the 

 hour-glass structure can be seen ; greenish-brown augite, showing 

 very distinct zonal structure. Very little olivine. 



Ground-mass: labradorite, '4 x '04 mm.. 42 per cent.; augite, 



