The Humber Bridge is a suspension bridge with the north tower sited on the high water line and the south tower founded in shallow water 500m from the shore. On the north bank, a hard well-jointed bed of chalk comes close to the surface and is covered by a tough layer of glacially deposited chalky boulder clay. The chalk has provided good foundations for both the anchorage and tower on this bank, on the south side, soft alluvium is underlain by beds of boulder clay, sand and gravel. Below these beds, at a depth of 30m, there is a deep bed of stiff, heavily fissured kimmeridge clay, on which the tower and anchorage have been founded. Designed to cross the last major unbridged estuary in Britain, the bridge comprises reinforced concrete towers aerial-spun catenary cables and a continuously-welded, closed – box road deck supported by inclined hanger cables.