BGS Seabed Sediments 250k (formerly BGS DiGSBS250k) indicate recent deposits commonly form a veneer or superficial layer of unconsolidated material on the seabed. Sediments are mapped using ship-board geophysical surveys and the map is based on seabed grab samples of the top 0.1 m, combined with cores and dredge samples as available. Sediments are classified into 15 classes, according to the proportions of sand, gravel and mud present.