Wealden district - The South Downs
The South Downs form a range of hills similar to the North Downs, except that they are bounded by a steep slope facing to the north and slope away gently towards the south (Plate P212516). Like the North Downs, they are composed of Chalk, but here it is up to 425 m in thickness.
The Chalk in Sussex is overlain by a relatively thin succession of younger bedrock layers (Palaeogene sediments), but unlike those found in Kent, these are composed largely of clay, with only minor sand, and they are mostly confined to a narrow belt within a down-fold or structural trough around Chichester. This clay succession is up to 130 m in thickness. Unlike the North Downs, the Chalk of the South Downs is underlain by thick sedimentary deposits that are a continuation of those making up the younger sedimentary bedrock in the Weald. Deformed older sedimentary bedrock similar to that found at depth beneath the Weald also occurs but mainly at depths of more than 1 km.