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  • The BGS Seabed Geology 10k: Anglesey digital map portrays the distribution of the different types of bedrock and sediments that are interpreted to represent the dominant geology within to the top 1-2 metres of the seabed to the north-west of Anglesey, at a scale of 1:10 000. It also includes the distribution of the main seabed morphological and geomorphological features (e.g. drumlins, sandwaves) and the principal structural features observed at rockhead (fractures). This digital map is the result of the interpretation of two high-resolution, multibeam echo-sounder (MBES) bathymetry datasets: (i) the Off Skerries HI1420 survey, collected by Net Survey in 2013 as part of the Civil Hydrography Programme (CHP) surveys managed by the Maritime and Coastguard Agency (MCA) for the UK Hydrographic Office; and (ii) the North St George’s Channel candidate Marine Conservation Zone (rMCZ) survey, collected jointly by JNCC and Cefas in 2012 for the Department for Environment, Food and Rural Affairs (Defra). MBES backscatter, physical samples (e.g. grabs, cores, and boreholes), academic papers and previous BGS geological interpretations at broader scales (250k and 50k scales) were used to further inform this geological interpretation. The bedrock is divided into three units: (i) Neoproterozoic to Palaeozoic age metamudstones and metasandstones of the Monian Supergroup; (ii) undifferentiated Lower Palaeozoic age rocks (mudstone, volcaniclastics, siltstone, slate); and (iii) limestone and sandstone of the Carboniferous Limestone Supergroup. The superficial deposits are composed of various types of glacial sediments (e.g. glacial till and morainic deposits) that were deposited underneath and around the margins of the last British-Irish Ice Sheet in the area, and also more recently deposited marine sediments.