as it does in smaller hills to the west including Dollis Hill itself. Further north, ridges of Claygate Beds overlain by the pre-glacial Stanmore gravel form the slightly broken-up Grim's Dyke Ridge: Mill Hill, Totteridge, Arkley and Monken Hadley, Elstree, and Stanmore and Harrow Weald Commons. Much of east and northeast London lies on the modern floodplain of the Thames (spared from flood by the Thames barrier) or older terraces, a notable interruption being the remains of the artificial Beckton Alps. Pole Hill at Chingford and Lippitts Hill near Gilwell Park are capped by small outliers of Claygate Beds, while the higher parts of Epping Forest such as High Beach are Claygate and Bagshot beds with later gravels. South London Faulting and folding brings the chalk close to the surface just south of the Thames in Lewisham and Greenwich. This has resulted in a notable ridge formed of Palaeocene deposits (the Lambeth Group), which includes Shooter's Hill, Greenwich Park and Blackheath. West of the valley of the Ravensbourne, this ridge continues as Telegraph Hill, Nunhead and Honor Oak, towards Denmark Hill. To the south Crystal Palace and Sydenham Hill lie on another outlier of Claygate beds. In south-west London the lower terraces of the Thames of its west stop abruptly at a notable bluff cut into the London Clay against Richmond Hill. The higher ground across the east, save for the broad valley of the Wandle is capped across northern Wimbledon and the Norwood Ridge by Claygate Beds and older Thames gravels; the broad western part of this is dissected by the valley of Beverley Brook, which separates Richmond Park from Wimbledon Common. Climate The climate of London is broadly similar to the rest of the UK, with warm summers, cool winters, no wet or dry season, and often moderate to strong winds. It is classed as a temperate maritime climate according to the Köppen climate classification system. In terms of the local climate profile, the temperature tends to increase towards the centre of the urban area, primarily because of the urban heat island effect, but also because London's topography results in the central area being the lowest part of the region in terms of altitude. Daytime winter temperatures in London are around , but can vary from as high as , down to as low as , as occurred during January 1987. Night time temperatures hover a little above