Liiuhurgite Roch. 127 



with a little interstitial brown glass. (See Plate XL., Fig. 1). 

 Felspar microliths consisting of labradorite of the medium type, 

 having an extinction angle of - 35 deg. Augite, chiefly occur- 

 ring in the ground-mass. The crystals are of long prismatic 

 habit, and of a deep hazel-broAvn colour. In the less dense 

 samples this mineral occurs ophitically intergrown with the 

 felspars. Average dimensions, .11 mm. x .023 mm. 



Diopside, rare ; a few phenocrysts present, of a pale green 

 colour, and with feeble pleochroisim. Several twinned crystals 

 occur in one of the slides, wbicli INlr. D. J. Mahony, M.Se., was 

 »ood enouofh to examine with us, and lie confirms our deter- 

 mination of this mineral. The presence of diopside may account 

 for the small percentage of Cr..O.^ recorded in the analysis 

 appended to this paper. Olivine, occurring, \Et — as phenocrysts, 

 short, stout prismatic, or of tabular habit, the largest having 

 a length of about 2 mm. ; 2nd — as rounded granules, their 

 shape being probably due to partial resorption by the magma. 

 The olivines are colourless to pale green, somewhat corroded 

 and often partially altered on the margins and along cleavage 

 planes to a dull olive green or yellow substance. Several large 

 phenocrysts of olivine exhibit a poicolitic structure, being filled 

 with minute included crystals of ilmenite or possibly (?) picotite. 

 (See Plate XLL, Fig. 4). The olivine also occasionally contains 

 strings of brown glass inclusions. 



Magnetite. — Abundant as small crystals disseminated through 

 the magma, and rectangular or triangular in section : some- 

 times occurring in linear series. This mineral shows a tendency 

 to form irregular zones around the olivine phenocrs^sts, and 

 especially the rounded granular crystals. (See Plate XLL, Fig. 3). 

 The magnetite is probably more or less titaniferous, as it 

 shows some translucency, being of a brown colour in very thin 

 sections by transmitted light. 



Ilmenite. — Some medium-sized tabular crystals, showing 

 skeleton structure around the margins, having a sub-metallic 

 lustre by incident light. (See Plate XL., Fig. 2). Numerous 

 minute truncated triangular crystals in this ground-mass are 

 also probably referable to the same mineral. 



Zeolites. — ^Analcite appears to be present as a transparent 

 isotropic mineral filling minute, irregular cavities, and often 

 penetrated by acicular crystals of natrolite. 



