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Sz Pak Wan - Sam Pak Wan - Yi Pak Wan. The sand beaches in Discovery Bay are well developed and slightlyelevated, indicating that they are probably storm beaches. They are composed of coarse sand and shell debris, witha transition offshore to grey mud with shells. A lagoon has developed behind the beaches, and mangrove flats areestablished on the tidal creeks.Peng Chan. Boreholes in Tung Wan (GIU 05202) revealed a succession of grey mud or sand overlying weatheredrock. Most of the bay is underlain by grey marine sand, 4 to 8 m thick, with shells and coral fragments. Thisdeposit is contiguous with the thin beach deposits around the bay. Weathered rock generally underlies the sand,although mud is recorded in places.Man Kok Tsui - Kau Shat Wan, The beaches along this promontory are sandy, with few boulders or cobbles.Storm beaches have formed up to 2 m above sea-level at the backs of the bays.Silver Mine Bay - Mui Wo. A wide sand beach encircles the back of the bay, behind which a lagoon has formed.This is now being reclaimed. West of the sandy beach at Mui Wo, boreholes have proved 5 to 7 m of dark greysand with shell fragments. This marine deposits overlies alluvium. It dies out 120 m west of the high water mark.Boreholes sunk in the new river channel (GIU 02444) show that it is underlain by grey silty sand with gravel, andsome shell fragments. Inland to the west, these marine sands pass into brownish-grey, silty alluvial sand withgravel In the east, the sand has been reworked and the fines removed to form a beach. Bedrock is generally atshallow depth, ranging from -12,6 mPD at the river fliouth, to -2.5 mPD about 1 km inland. Many boreholesintersect, or were terminated at boulders, believed to be the relict of extensive slope deposits beneath the alluviumand marine deposits. The marine sands are generally thin, ranging up to 7.5 m thick, and are underlain by up to 4 mof brownish-yellow, alluvial silty sand. About 1 km southeast of the ferry pier, the marine deposit comprises about7 m of dark grey silty sand with shell fragments, overlying thin mottled alluvium or weathered bedrock.Cheung Chaw. The two granite islands are connected by a raised sand bar, or tombolo, forming a textbookexample of dumbbell islands. The sand composing the bar has a coarse, gravelly texture, and rises up to 4 mPD atits crest.Pui O Wan. The area between Pui O village and the beach is dominated by low-lying alluvium, rising gentlyinland from 2.9 to 4.8 mPD. Much of the area immediately behind the beach is waterlogged. Alignedwestnorthwest across the alluvial plain, about 200 m behind the present beach, is a sand bar 300 m long and 50 mwide. This bar has been stranded by alluviation of the lagoon (Plate 46). The crest of the present beach" is at 4 to4.5 mPD, and is composed of clean white sand. The beach slopes gently seawards and becomes progressivelymuddy below high water mark (Plate 47). Seven boreholes in the raised bar at +4.5mPD (GIU 06626) intersected2.5 to 4 m of loose, light brown, fine sand with some shell fragments, overlying 7 to 9.5 m of grey marine sand. Thebase of the succession is at about -7mPD, Below these sands are 10 to 20 m of alluvium, comprising clayey siltysand with gravel and boulders, which is yellowish-brown, and poorly stratified, lying on tuff bedrock.Cheung Sha. An extensive sandy beach at Cheung Sha extends along the gently embayed coast for almost 3 km. Itis composed of clean, pale yellow sand, is up to 50 m wide, and shelves gently below low water mark.Tai Long Wan - Fan Lau Tung Wan - Fan Law Sai Wan. Long sandy beaches occur at Tai Long Wan, Fan LauTung Wan and Fan Lau Sai Wan at the back of wide, sweeping bays in the steep coast (Plate 48). The beach atTung Wan has been modified by the construction of a breakwater and the Shek Pik Prison. All the beaches alongthis coast are composed of well sorted, fine- to medium-grained, clean quartz sand.Intertidal DepositsHolocene estuarine intertidal deposits are of mixed alluvial and marine origin. They generallyconsist of grey clayey silty sand with plant remains, and dark grey, organic clayey silt with shellfragments, and accumulate as mud flats in wide embayments, between the high and low watermark. Mud on wide interfluves between branching distributaries is commonly rippled. Channelsgenerally have a sandy bed, and sand splays and ribbons cross the flats. Mangrovescharacteristically grow on the flats and channel margins. The deposits predominantly consist ofgrey, clayey silty sand in the channels, and dark grey, organic, clayey silt with plant remains andshell fragments on the flats. Flaser bedding is common. Intertidal deposits are most extensive atTai 0 and Tung Chung.117