Worth. — Petrological Notes on South Victoria ImhU Jiorks. 49i 



visible ; greatest observed length, 2-5 mm. A few glancing spots of feld- 

 spar can be seen. Groundmass is felted feldspar, with an occasional larger 

 individual, rather ill defined (symmetrical extinctions appear in some 

 instances to indicate anorthite). The ground is a very pale buff in colour, 

 scarcely distinguishable as tinted, except by contrast with the larger colour- 

 less feldspars. There are fairly numerous small prismatic forms of aegirine, 

 with an occasional larger crystal rendered practically opaque by magnetite. 

 With the one-inch objective and careful lighting a clear mineral in very 

 minute forms may be seen to be distributed throughout the slide ; with 

 the ^-inch this is seen, in part at least, to possess hexagonal outline. On 

 treatment with HCl followed by fuchsin the slide takes the dye locally, 

 and thus indicates that the mineral last mentioned gelatinizes in the acid. 

 The grains are then found to be parts of larger crystalline areas marked out 

 by the cleavage -cracks therein. Identification as nepheline appears certain. 

 This is the more probable since the acid which has been in contact with the 

 slide yields, on evaporation, cubic crystals and aluminium-chlorides. There 

 are some small porphyritic feldspars (the largest under 2 mm. in length), 

 several of which show polysynthetic twinning, while the constituents of 

 the groundmass frequently bend around them in flow form. Phonolytic 

 trachyte. From crater. See official specimen 607, page 115, from which 

 it difEers slightly, especially in being hard and compact. 



Broivn Island, 2. — ^A black very compact rock, with augite and olivine 

 visible here and there. The specimen is slaggy at one angle. A rock 

 almost opaque, with granular magnetite. Fairly frequent lath-shaped 

 feldspars, ragged at the ends, and showing closely repeated twinning. 

 Brown augite, in small crystals, is by far the most prominent mineral in the 

 groundmass ; it shows no pleochroism. The magnetite inclusions in this 

 mineral are comparatively few. The slide shows one larger augite, cracked 

 across the centre, and parted by a belt of the groundmass. The two parts 

 thus formed have each a central area of bright green and a complete border 

 of pale brown. The positions of extinction of the green and brown differ 

 by about 7° ; neither is pleochroic. Olivine is common, both in larger 

 and smaller forms. It sometimes achieves good crystal outUne, and, 

 although rather free from inclusions, intrusions of the groundmass do 

 occur in it, as also do the largest and best-formed crystals of magnetite 

 which the slide presents. Basalt. From summit of island, in situ. 



Brown Island, 3. — Light yellowish-brown rock ; hard, but of open 

 texture ; appears slaggy under hand-lens. Vesicular, a brown glassy base 

 of very feeble aggregate polarization. Lath-shaped feldspars, from sym- 

 metrical extinctions probably oligoclase. Some of the larger forms show 

 very closely repeated twinning, and also considerable inclusions of glass. 

 Some are quite clear in the centre of their length, but crowded with granules 

 and microliths toward either end, finally dying away into the gromidmass. 

 There is a little brown hornblende, and magnetite in small crystals and dust. 

 At places the vesicles have a narrow lining of zeolite. Andesite. Near 

 top of south peak of island, in situ. 



Brown Island, 4. — Two specimens of slaggy vesicular basaltic lava, 

 very open textured, the one a rich brown, the other largely yellow-green. 

 The fracture of the green specimen is black. 



ia. — Highly vesicular, a rich-brown glass, almost opaque, red by reflected 

 light. Ohvine the only porphyritic mineral, except for the presence of a 

 single rod of feldspar. 



