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Detailstal O. Alluvial deposits form a narrow strip (046 128) on the floor of the main valley at the base of an extensivesheet of slope deposits below Sze Shan. They are rich in cobbles and boulders, being mostly reworked slopedeposits from which the fines have been removed. Alluvium also forms a terrace (039 131) in the west of the inletand underlies a large area of enclosed fields (042 123) as a fan delta to the south.jSham Wat Wan - Sha Lo Wan. Alluvium in the Sham Wat Valley occurs as a very narrow strip, with isolatedoutliers of raised Pleistocene alluvium forming flanking terraces (065 142). In the Sha Lo Wan Valley, alluvium isdeveloped as a small fan delta at the base of an extensive debris deposit (079 167).Tin Sam. The Tin Sam delta (101 167) occurs at the mouth of the small stream draining from the hills to the westof Tung Chung. The fluvial deposits of the delta extend offshore, and have been modified by coastal processes toform a fringing sandy beach. The alluvial plain is mostly at around 5.5 mPD. Two boreholes in the delta (NL39and NL40, GIU 04459) intersect a complex interbedded sequence that includes marine deposits. In borehole NL39(1019 1670) a dark grey, clayey silt layer about 3 m thick, and of probable marine origin, lies below 10 m of silt,sand and gravel with some clay of probable alluvial origin. In borehole NL40 (0990 1690), a 4 m-thick layer ofdark grey sand and clay underlies 8 m of cobbles, boulders and gravel in a clay matrix with clay horizons.Chek Lap Kok (prior to development). Up to 8 m of sand and gravel formerly rested on weathered granite in anextensive alluvial tract at Sham Wan Tsuen (115 194), The deposit widened down the valley, dropping from atleast 7.5 to 3.0 mPD. One borehole (L15/3427A, 1150819528), situated at Sham Wan Tsuen, intersectedalluvium. This recorded 7.5 m of light, yellowish-grey ,clayey sand with some fine gravel. This site was removedby the airport development works.Tung Chung. The most extensive deposits of alluvium in the district occur in the east and west streams of theTung Chung Valley. Pleistocene alluvium infills the western valley to form a raised terrace from 400 to 500 mwide, and extending inland for about 2000 m. It reaches an elevation of almost 20 mPI), forming an extensive,northerly-inclined surface covered with fields on the valley floor. The terraces grade up into coarse, bouldery debrison the surrounding slopes and, except where there is a marked break in slope, the boundary is difficult todistinguish. Few sections expose the deposit, but away from the foot of the hillslopes, where the material is coarseand contains cobbles and' boulders, the deposit is mottled red and yellow sandy silt with some sand lenses andlayers. Holocene alluvium form a series of narrow strips, less than 100 m wide, adjacent to the modern streamchannel incised in the older terrace by up to 3 m.Alluvium in the eastern valley is very restricted. A thin, continuous strip of alluvium lines the modem channel withdetached remnants of the Pleistocene alluvium forming isolated terraces along the valley sides. The combineddeposits are less than 100 m wide.The alluvial fan at Ma Wan (113 150) comprises the eluviated distal extremities of adjacent slope deposits. It isdominated by cobbles and boulders, and has been incised by a recent stream, The deposit is narrow, and is fringedby Holocene beach sand and mangroves. The surface of the fan is exposed in the intertidal region. It is probably oflate Pleistocene age.West Brother island (prior to development). The southern tip of the island was dominated by a cobble beach(246 211), which formed the reworked part of a debris fan from the centre of the island. The slope deposit,possibly fluvial in part, was well exposed near the mine, where it was preserved beneath a concrete platform.Pak Mong. An extensive area of flat, coastal alluvium (150 176) grades inland into slope deposits that feed downthe two valleys.Ngau Tau Wan - Tai Ho Wan. Behind the eluviated, raised sandy beach is a mangrove swamp that mergessouthwards into an alluvial flat (159 172). The boulder-strewn river channel cuts down into this flat by 2 m ormore. A sharp break of slope indicates the base of the surrounding slope deposits,Yi Pak- Discovery Bay. Very fewmappable deposits of alluvium occur on the northeastern end of Lantau Island.Several minor deposits were identified at Tso Wan (237 218), Fa Peng (237 213), Pa Tau Kwu (236 203), Penny's? (2 A 25^° 4 *** 215 2 ° 9) md Sam Pak °" 191) " ^lar^est m at Yi Pak 0 W Ig5 >«"»livery Bay (194178). At Yi Pak, the deposit is a fan at the seaward end of an extensive, dendritic valley-fill debris deposit that hasacctoulated behind a raised bar feature at the back of the bay, The stream has an outlet against the hillside.Similarly, at Discovery Bay, the alluvium is backed up behind a raised bar, the stream flowing southwards at thefoot of the hillslope behind, and parallel to the bar, Tributary valleys are filled with debris deposits, The deposithas now largely been covered with fill as part of the Discovery Bay residential development,110