(2) Rocks with a little felspar and characterized by large poikilitic plates of hornblende. These contain abundant pyroxene, and some olivine, apatite and magnetite. (3) Rocks with long, thin blades of hornblende in a fine-grained matrix of labradorite, and with some patches of black “glass” and abundant minute prisms of apatite. In hand specimens these look like dyke-rocks, but I think the texture and the patches of magnetite show that they are segregations. (4) Coarse-grained rocks with perhaps more felspar than hornblende. Hornblende in large crystals in a matrix of labradorite. The texture is coarser than in the preceding type. Felspars reach 2 or 3 mm. in diameter. The hornblende includes some small crystals of yellow pyroxene. Apatite and magnetite are given abundant. All four types appear to be closely inter-related. They contain the same minerals in varying proportions and probably grade one into the other. The obsidian and the pieces of red glass are basalt glass, and are probably similar to the specimen described by Renard in the Report on the _Challenger_ Collection, p. 82. He states that the inhabitants use the rock for striking fire. OBSERVED SECTION FROM THE PEAK TO HERALD POINT _Elevations._ _Rock provisionally named._ _Remarks._ FEET 6,400 Scoriæ and vesicular basalt. Forming summit. 6,200-5,700 Loose scoriæ and bombs. Crater cone. 5,700-5,500 Basalt. 5,000-4,550 Trachy-basalt. 4,400 Vesicular basalt. 4,300 Trachytic agglomerate. 4,250 Compact basalt. 4,150 Red scoriæ. 3,950 Basalt. 3,750 Scoriæ. 3,600 Scoriæ and basalt. A contact. 3,520 Basalt and scoriæ. A contact. 3,420 Scoriæ and basalt. A contact. 3,220 Grey basalt. (Break in the observations). 1,200 Basalt and scoriæ. A contact. (Break in the observations). {This rock is used for 225 Basalt. { building the dwellings { by the inhabitants. 223 Cinder. 222 Scoriæ. 220 Tuff. 216 Agglomerate. To sea Compact basalt. Rough columnar level. structure. A number of vapour vents were observed at different points. It is apparent that the small craters mentioned above as existing on the settlement plain sprang up after the main period of eruption when the island was built. To the west and about 22 miles from Tristan there are the four islands—Nightingale, Middle, Stoltenhoff and Inaccessible. NIGHTINGALE _Topography_