The North Sea Basin (or NW European Tertiary Basin) is by far the largest Tertiary basin in NW Europe. The main depocentres (apart from localized halokinetic subsidence features) are in the central and northern North Sea. The Tertiary North Sea Basin lies between the Variscan and Caledonian massifs of the Pennines, the Scottish Highlands, Fennoscandia and the Rhenish-Bohemian Massif. It is centred on a series of Mesozoic rifts running through the North Sea, which are the sites of the greatest water depths and the highest rates of sedimentation (Figs 9 & 19). Most of this area is characterized by marine sediments, probably with relatively narrow peripheral areas of marginal-marine and non-marine sediments: these have now largely been eroded by basin margin uplift, except around the southern and SE margins of the Basin.