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Sunset Peak MemberThe Sunset Peak Member is defined for the first time in this memoir. It coincides in part withagglomerate outcrops mapped by Allen & Stephens (1971) on both Sunset Peak (Tai Tung Shan)and Lantau Peak (Fung Wong Shan). The member is almost entirely pyroclastic and dominantlycomprises tuff-breccia and lithic lapilli-bearing tuff, but also includes eutaxitic tuff. A notablecharacteristic is the flattening of clasts, which imparts a planar fabric.The member only crops out in restricted areas on the highest peaks in east Lantau Island. Its typelocality is the summit (1336 1305) of Sunset Peak, where it is about 50 m thick. There is asmaller outcrop on a lower peak to the east, and substantial exposures occur on, and around, LinFa Shan, where the member is less than 70 m thick. An isolated outcrop around the summit ofLantau Peak is less than 100 metres thick.DetailsSunset Peak (Tai Tung Shan). Lapilli-bearing tuff and tuff-breccia form much of the summit of Sunset Peak, thetype locality of the member. On the summit (1318 1317), the tuff is poorly banded and includes quartz crystals upto 8 mm, and a few pebble-like lithic lapilli set in a fine ash matrix. Although exposures are mostly exhumedcorestones, the banding is generally sub-horizontal. Tuff-breccias near the summit (Plate 16, 1336 1305) are lightgrey when fresh, and contain clasts of vitric tuff or lava, up to 1 m across, although most clasts are less than 60 mmacross. There are also rare volcanic lava bombs, and the matrix consists of crystal-bearing vitric tuff. A eutaxiticvitric tuff occurs locally (1345 1306), and is dark grey, with flat, streaky pumice lapilli which are visible onweathered surfaces. Its dominantly vitric matrix contains a few quartz and feldspar crystals up to 2 mm across. Atthe base of the member, there are tuffaceous siltstones and mudstones, but their contact with the underlyingsuccession of mainly lava and tuff is not exposed.East of Sunset Peak, there are exposures (1446 1389) of lithic lapilli-bearing crystal tuff or tuff-breccia., similar tothose on both Sunset Peak and Lin Fa Shan. The pock-marked surface of the light, brownish-grey bouldersindicates the presence of abundant, rounded lithic clasts. In tuffs (1432 1332) to the west, rounded lapilli of vitrictuff, or lava are up to 30 mm across. The matrix is comprised mainly of coarse ash crystals, and there is anindeterminate layering defined by clast orientation.Lin Fa Shan. On the summit (1502 1514), light grey, lapilli-ash crystal tuff with a fine ash matrix includes lithiclapilli which weather preferentially, leaving elongate hollows (Plate 17) up to 50 mm long. Fabric in the corestonesappears to dip to the east at 40°. Elsewhere on the summit, fabric is poorly developed, but the rock containsangular tuff blocks, up to 300 mm across, which weather preferentially. The slopes to the south are dominated bydisplaced boulders of elongate lapilli- and block-bearing tuff. The member is underlain by tuffaceous sandstone.Although the contact is not exposed, it may be locally unconformable. The succession is preserved in a synclinalcore, whose northerly-trending axial plane passes through the summit.Lantau Peak (Fung Wong Shan). South of the summit of Lantau Peak (0975 1217), the member comprises ablock- and lapilli-bearing vitric tuff. The blocks, which are up to 250 mm across, are set in a dominantly vitricmatrix which contains ash crystals. On the eastern ridge of the peak, the block-bearing tuff, or tuff-breccia,contains sub-rounded blocks up to 200 mm across, and on the northwestern ridge (0960 1244), the blocks define asub-planar surface. In the crystal-bearing vitric matrix, there is also a streaky eutaxitic fabric which dips 45° to thenorthwest. The member overlies porphyritic rhyolite lava and pebbly tuffite, and is capped on the summit by poorlybanded, porphyritic rhyolite lava.PetrographyThe typical block-, and lapilli-bearing tuff has a welded matrix (HK7886, 1500 1418) thatincorporates subhedral to broken crystals. Small quartz crystal aggregates suggest eitherrheomorphism of the vitric matrix, or a pyroclastic origin from a lava-dominated vent. Thematrix of vitric tuff from Sunset Peak (HK8432, 1337 1328) is vitroclastic and containsabundant, small, strained shards, and some well-defined, broken bubble-shaped shards. There aresmall, subhedral to euhedral quartz and feldspar crystals, which are generally less than 2 mmacross. The feldspar is partially replaced by chlorite and calcite. Typical tuff-breccia from thetype locality on Sunset Peak (HK 8435, 1336 1305) is light grey, with clasts up to 1 m across,set in a crystal-rich vitric matrix. Most of the pyroclasts are broken, and in thin section there are57