Greensand Ridge - Relief and Drainage

Relief and Drainage

Broadly speaking, the Greensand Ridge runs along the northern edge of the Weald in a west-east arc from Surrey into Kent, just south of and parallel to the chalk escarpment of the North Downs. The ridge is separated from the North Downs by a fertile vale, the Vale of Holmesdale, formed on Gault Clay, and a narrow band of Upper Greensand that outcrops at the foot of the chalk scarp. In some places the clay vale is very narrow: for example at Oxted the gap between the Greensand Ridge and the North Downs is less than 2 kilometres (1.2 mi).

The Greensand Ridge, capped by the resistant sands and sandstones of the Hythe Beds, reinforced by bands of chert, rises steeply as a series of high, wooded escarpments between Gibbet Hill, Hindhead (272 metres (892 ft)), north of Haslemere, and the ridge's highest point, Leith Hill (294 metres (965 ft)). It then flattens for several miles, before re-emerging east of Nutfield to run eastwards as a high wooded ridge into an area between Oxted and Sevenoaks known locally as the Chartlands, where it reaches another high point at Toys Hill, Kent (235 metres (771 ft)). Here there are stunning views to the south of the Weald from a terrace donated in 1898 by Octavia Hill, one of the founders of the National Trust. The ridge continues eastwards past Sevenoaks, until south-west of Maidstone it is broken by the valley of the River Medway. The ridge then continues as far as Pluckley, Kent. From there the land levels until it drops to the old sea-cliff line above Romney Marsh.

In the area around Haslemere local anticlinal features are superimposed on the main axis of the Wealden anticline, causing the outcrop of resistant Hythe Beds to widen from 2 kilometres (1.2 mi) to more than 12 kilometres (7.5 mi) and to produce an escarpment that is particularly marked between Haslemere and Midhurst, where Blackdown rises to 280 metres (920 ft), the highest point in Sussex. South of here the Vale of Fernhurst has been eroded down into the Low Weald by what is now a small stream following a line of a gentle west-east trending upfold. This stream, the River Lod, runs parallel to the larger River Rother which flows about 10 km further south in the lee of the chalk escarpment of the South Downs. Valley slope processes in the Vale of Fernhurst have resulted in escarpments to the north and south that are steep enough to have collapsed by land slipping. Further east, the Lower Greensand has not produced any pronounced topographical features.

In many places along the escarpment of the Greensand Ridge erosion by wind and rain, landslips on the steep scarp face, and solifluction in glacial times have further combined to create steep-side coombes, and low hillocks below the scarp.