488 Transactions. 



structure. The rock appears vesicular, with the vesicles sometimes com- 

 pletely, sometimes only partiallv, infilled with a zeolite, which is probably 

 analcime. Many of these zeolitic areas have, however, the di.-.tinct appear- 

 ance of being pseudomorphs after some previously existing mineral, and 

 liexagonal sections for ths latter are fairly clearly indicated here and there, 

 mth residual patches of unaltered mineral which may well be nepheline. 

 The extremely small percentage of augite is noteworthy. Treatment of a 

 section with HCl followed by fuchsin produces differential staining. The 

 groundmass becomes bright red, the feldspars remain water- white, and 

 the zeolite areas take a violet shade. It then becomes clear that these 

 latter are in many cases very certainly replacements of a mineral of hex- 

 agonal form. The straining of the groundmass also throws into relief 

 numerous thread-like feldspars of a smaller order than the lath shapes, 

 which alone are clearly discernible in the unstained specimen. The HCl 

 which has been in contact with this rock is stained with iron, and yields 

 on evaporation deliquescent crystalloids with cubes of sodium-chloride. 

 The other chlorides apparently include that of aluminium^ Phonolitic 

 trachyte (altered). Apparently official specimen 803. 



Inaccessible Island, 3. — Purple-brown trachytic texture, rather com- 

 pact. The ground a rich-brown glass, with some magnetite. Very nume- 

 rous lath-shaped feldspars fairly well terminated, and frequently showing 

 a line of inclusions of groundmass down the centre. There are also smaller 

 much-attenuated feldspars. The laths as a whole have one general direc- 

 tion. Larger feldspars, rectangular and rhomboidal, occur ; these are 

 mainly associated in groups of two or three, in contact with each other 

 and partly intergrown, and show considerable glass inclusions, but only in 

 one case polysynthetic twinning. No nepheline or zeolite is discoverable, 

 hut the rock is in many respects much like Inaccessible Island, 2. Trachyte, 

 probably phonolitic. Apparently official s])ecimen 802. 



Black Island. 



The first camp here was pitched about the middle of the eastern side 

 of the island, not far from where the party landed. The specimens Nos. 2 

 to 7, 9, 10, and 14 were all taken from a " rubble-heap " a few yards from 

 the tent. This so-called heap was an area some 20 yards by 3 yards, and 

 none of the specimens were in situ. 



Black Island, I. — ^Dioritic texture, dark brown and practically white 

 crystals. Brown augite, ophitic, diallagic in parts. The margins frequently 

 darkened, sometimes with the development of a rich-brown pleochroi(; 

 mineral. A few crystals are partially altered to uralite. Much feldspar, 

 a,pparently all labradorite. Considerable areas of micro-pegmatite, in which 

 Ihe feldspar is always clouded. A sprinkling of ilmenite and some apatite. 

 Q.uartz-augite-diorite. From half-way up peak of island, not in situ. 



Black Island, 2. — Coarse-grained granite, pink feldspars, apparently 

 ])recisely like Erebus, 3. 



Black Island, 3. — Very fine-grained pale-grey rock, slightly mottled. 

 Much white mica in minute brightly sparkling form. Groundmass micro- 

 felsitic, with minute sericitic mica. A few scattered grains of magnetite. 

 Scattered blades and grains of olive-green hornblende, some of which shows 

 striking pleochroism from olive to vivid blue-green. The porphyritic con- 

 stituents are patches of much-clouded white feldspar, and quartz in sharply 



