Landscape Types : Chalk Landscapes
2.0 Chalk Landscapes
Chalk, laid down towards the end of the Cretaceous period, is a relatively homogeneous rock, divided on a lithological basis into three formations: Upper, Middle and Lower Chalk. However, in most parts of the South Downs, it is not possible to differentiate between formations of Middle and Upper Chalk. Upper Chalk is characteristically embedded with flints and predominates throughout the South Downs; Lower Chalk is only exposed in a band along the foot of the escarpment. In some areas, the chalk bedrock is overlain by more recent superficial deposits. The most significant, Clay-with-Flints, a reddish-brown sandy clay deposited during the Tertiary period, is usually found in patches on the more elevated parts of the chalk dip slope.
The chalk landscapes of the Sussex Downs AONB form an impressive steep ridge extending eastwards from the Sussex-Hampshire border to the coast at Beachy Head. This outcrop of chalk is a southerly remnant of a once more extensive area of chalk which formed a massive dome stretching across the Weald to the North Downs. The central Wealden portion of chalk was later removed by erosion in the Tertiary period leaving two curving outer limbs, the North Downs and the South Downs.
The South Downs consist of a chalk dip slope inclined to the south with a dramatic north-facing escarpment. Earth movements and subsequent erosion towards the end of the Cretaceous period resulted in the uplift and folding of the chalk to influence the present day complex, undulating relief and produce a particularly wide range of chalkland scenery.
The chalk dip-slope has been eroded by numerous small dry valleys and the entire mass of chalk has been carved into separate blocks by the principal chalk valleys, four of which contain the rivers flowing from the Weald to the sea. (ref. principal river floodplains.)
The chalk landscapes of the AONB can be broadly divided into three categories:
• The chalk uplands of the south-facing dip slope
• The chalk valleys
• The chalk escarpment
