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ForewordThis memoir describes the geology of Lantau and adjacent islands, including Chek Lap Kok, TheBrothers, Ma Wan, Tsing Yi, Peng Chau, Hei Ling Chau, Cheung Chau and The Sokos. The area ofNorth Lantau and Chek Lap Kok were during preparation of the memoir, sites of major civilengineering works related to Hong Kong's new airport. Consequently, some features described here arenow obliterated.The geology described is shown on 1:20 000 scale sheets 9 (Tung Chung), 10 (Silver Mine Bay), 13(Shek Pik) and 14 (Cheung Chau). The memoir forms part of the published results of a programme ofsystematic geological mapping undertaken by the Geotechnical Engineering Office (GEO), formerlyGeotechnical Control Office (GCO), between 1983 and 1992. The programme has studied the onshoreand offshore geology of the Territory in far greater detail than previously attempted. These geologicalmaps and memoirs have enhanced our understanding of Hong Kong's stratigraphy and structure, andhelped to establish a geological database necessary for the continuing economic development of theTerritory. The mapping programme was undertaken by the Geological Survey Section of the PlanningDivision of the GEO. The section was led by Mr P. J. Strange, Dr R. Shaw, Dr I. R. Basham and Dr C JN Fletcher during the periods of mapping and compilation of this memoir and its accompanying maps;the Division was under the direction initially of Mr R. K. S. Chan and latterly Dr R. P. Martin.The onshore geological survey of sheets 9 3 10, 13 and 14 was largely undertaken by Dr R. L. Langford,the principal author of the memoir, from 1988-92. Tsing Yi and Ma Wan were mapped by Dr R.Addison in 1986, and part of the Tsing Chau Tsai peninsula on Lantau was mapped by Mr P. J. Strangein 1987. In 1985 Mr Strange also mapped Ching Chau (Green Island) and Lamina Island, andpublished his findings in Memoir 2 of this series. Parts of Sheets 9 and 10 were remapped in 1991 at1:5 000 scale by Mr P. A. Kirk and Dr RJ.Sewell, and their early findings have been taken into accountin this memoir. The principal authors of the sections on structural geology and major intrusions are MrKirk and Dr Sewell respectively. Dr R.Shaw and Dr S.D.G.Campbell are respectively principal authorsof the sections on onshore superficial deposits and weathering, and metamorphic geology. Offshoregeology for Sheets 9, 10 and 13 was compiled by Mr J. W. C. James between 1990 and 1993. Sheet 14was compiled by Dr R.Shaw and Mr J.A.Fyfe in 1992-3. Mr James and Dr Shaw are the principalauthors of the section dealing with offshore deposits. Final compilation of the memoir was undertakenby Dr Campbell. Dr Langford, Dr Addison, Mr Strange, Mr James, Mr Fyfe and Dr Campbell wereseconded to the Hong Kong Government by the British Geological Survey.Previous studies of the district were carried out within the Geotechnical Areas Studies Programme(GASP) of GEO. Reports in this series covering the district, present geotechnical information on slopes,terrain, geomorphology, vegetation, land use and erosion. These studies used solid rock geology shownon the 1:50 000 map of Allen & Stephens (1971). This memoir and the four accompanying map sheetssupersede both the solid and superficial geology maps presented in the GASP reports.The geological field survey benefitted from the co-operation of various organizations and manyindividuals. The Government Flying Service (formerly The Royal Hong Kong Auxiliary Air Force)provided helicopter transport to remote and rugged locations. The Marine Department and Royal HongKong Police supplemented commercial boats used to map the coastline and many small islands. Landtransport was mostly supplied by the Islands District Office, City and New Territories Administration,and Highways Department. Latterly, the Provisional Airport Authority provided assistance with accessto areas scheduled for development related to Hong Kong's new airport. The co-operation of Electronicand Geophysical Services Ltd in compiling the offshore geology is also acknowledged.This memoir, and its accompanying map sheets, will be of interest and value to engineers and planners,to those concerned with resource investigations, to educationalists and earth scientists, and to interestedmembers of the general public.A. W. MalonePrincipal Government Geotechnical Engineer