North Downs

Coordinates: 51°16′N 0°30′W / 51.267°N 0.500°W / 51.267; -0.500
Source: Wikipedia, the free encyclopedia.
Not to be confused with North Wessex Downs.

North Downs
The North Downs near the entrance to the Channel Tunnel in Folkestone
Highest point
PeakBotley Hill
Elevation270 m (890 ft)
Naming
EtymologyOld English dūn, meaning 'hill'
Geography
CountryEngland (United Kingdom)
RegionSurrey, Kent
Parent rangeSouthern England Chalk Formation
Geology
OrogenyAlpine orogeny
Age of rockCretaceous
Type of rockchalk

The North Downs are a ridge of

Kent Downs. The North Downs Way National Trail runs along the North Downs from Farnham to Dover
.

The highest point in the North Downs is

Westerham Heights, Bromley, the highest point in Greater London
at an elevation of 245 m (804 ft).

Etymology

'Downs' is from Old English dun, meaning, amongst other things, "hill". The word acquired the sense of "elevated rolling grassland" around the 14th century.[2] The name contains "North" to distinguish them from a similar range of hills – the South Downs – which runs roughly parallel to them but some 50 km (31 mi) to the south.

Geography

Geology of the South East, chalk is light green (6)
View from North Downs towards Reigate

The narrow spine of the

Vale of Holmesdale at the foot of the escarpment, in which the underlying stratum is primarily gault clay. The northern boundary is less apparent but occurs where the chalk submerges below the more recent Paleocene deposits.[1]

The Downs are highest near the Kent–Surrey border, often reaching heights in excess of 200 m (660 ft) above sea level at the crest of the escarpment. The highest point is

Medway Valley the Downs become broader and flatter, extending as far as the Isle of Thanet
.

The ridge of the North Downs is intersected by the valleys of a series of rivers: the

Betchworth, Caterham, Lyminge and Hawkinge. Except for the river valleys and wind gaps, the crest of the escarpment is almost continuous along its length. The dip slope is dissected by many small dry valleys, and in the broad eastern part in Kent, by further river valleys such as that of the Little Stour
.

Leith Hill (the highest point in Surrey) is sometimes incorrectly referred to as part of the North Downs, but it is located on the parallel Greensand Ridge[7] and does not consist of chalk.[8]

Geology

Rock types

The Downland of the North Downs consists of distinct lithostratigraphic units (the types of strata, the names of which are always capitalised):

  • Shallow layers of sand and gravel are associated with areas of heathland, including at Headley and Netley Heaths in Surrey. These deposits have their origin in the Quaternary and indicate the position of the sea shore during this period.[9]
  • Clay-with-Flints, a sandy clay with many flints is found on higher ground. The origins of this layer are uncertain, however the clay is thought to have been formed during several periods of glaciation and was produced by cryoturbation and decalcification of the chalk.[10] This hypothesis is supported by the presence of flint, which is also found in the underlying strata.[10][11]
The exposed chalk workings of the former Betchworth Quarry on the south-facing scarp slope of Box Hill.

Wealden uplift and erosion

Weald Anticline
, and relating it to the towns of Kent

Following the Cretaceous, the sea covering the south of England began to retreat and the land was pushed higher. The Weald (the area covering modern day south Surrey, south Kent and north Sussex) was lifted by

dome-like structure was drained by the ancestors of the rivers which today cut through the North and South Downs. The dome was eroded away over the course of the Cenozoic, exposing the strata beneath and resulting in the escarpments of the Downs.[13][14]

Chalk is a relatively soft rock that may be eroded or weathered in a number of different ways. It is porous, absorbing up to 20% of its dry weight in water,[15] and is therefore highly susceptible to weathering by freeze-thaw action, which may occur over repeated annual or diurnal cycles. This frost weathering produces a mix of rubble and viscous mud, which may be washed downhill, further eroding the landscape (a process known as solifluction).[16] Since chalk contains a very high percentage of calcium carbonate, it can be dissolved by both groundwater[16] and rainwater.[17]

Across much of the North Downs, the chalk dips below the London Clay at a relatively shallow angle (c. 18° near Dorking), however at the far west of the range, local faulting has produced a much steeper angle (up to 55°), resulting in the distinctive Hog's Back between Farnham and Guildford.[18]

Ecology

Bee (left) and fly orchids (right) growing on the south-facing scarp slope of the North Downs in Surrey.

The North Downs support several important habitats including chalk grassland, scrub, woodland and chalk heath.

Chalk grassland

Medway Valley is dominated by upright brome and fescue, whilst grassland to the east is dominated by tor-grass.[1]
Owing to the close proximity of the North Downs to the European continent, the warm climate and the south-facing escarpment, several plant species survive on the chalk grassland which are scarce or not found elsewhere in the British Isles.

The nationally rare

late spider orchid is limited within the British Isles to chalk grassland between Folkestone and Wye. One of the two native British sites for the nationally rare monkey orchid is on the North Downs. The nationally scarce man orchid is not uncommon on chalk grassland on the Downs in Surrey and Kent. Other scarce plant species such as early gentian, dwarf milkwort and bedstraw broomrape
also occur on chalk grassland in the North Downs.

Marbled white (left) and Adonis blue (right) butterflies photographed at Denbies Hillside (part of the Hackhurst and White Downs SSSI) near Dorking.

Chalk grassland also supports a rich fauna, particularly insects. Notable butterfly species include

fiery clearwing moth and the straw belle moth
.

Quarries and chalk cliffs

On the summit of the cliffs between

great crested newt. The scarce musk orchid has colonised disused chalk pits near Hollingbourne in Kent.[20]

Woodland

Woodland was far more extensive on the North Downs prior to human clearance 5000 to 4000 years ago.[1] Fragments still remain particularly where the layer of clay-with-flints overlying the chalk has inhibited clearance.[21] Where this is the case species such as pedunculate oak predominate, although much woodland has been replanted with conifer and sweet chestnut.[1]

Lady orchids growing in calcareous woodland and scrub, Denge Wood.

Calcareous woodland occurs on thin soils where chalk is close to the surface. These conditions are most often found on the escarpment of the North Downs and on valley slopes, but may also occur on the plateau of the dip slope. Calcareous woodland is typically dominated by beech, hornbeam, yew and ash. Box Hill has one of the largest areas of native box woodland in England. One notable species characteristic of calcareous woodland is the nationally scarce lady orchid, which is found in more than 100 sites on the Kent stretch of the North Downs, but is confined to just two sites elsewhere in the UK.[22]

Scrub

Although its spread is often considered undesirable, scrub provides valuable habitat for a range of invertebrates, including the Roman snail, rufous grasshopper and the dark green fritillary.

Chalk heath

In Surrey, superficial deposits from the Quaternary are found overlying the chalk. These sands and gravels indicate the position of a former sea shore. Where these deposits occur, they are thin and the chalk also comes to the surface in the same areas (e.g. Headley Heath on the north east side of Box Hill), allowing acid-loving plants to thrive alongside those that prefer alkaline conditions, producing the rare chalk heath habitat.

History

Worked flints and human and animal remains dating from the

microliths and other implements discovered.[21]

Aylesford, Kent
, was constructed circa 4000 BCE.

In about 3000 BC the emergence of

Coldrum Stones, are constructed of sarsen stone, locally found on Blue Bell Hill and in the valleys of the dip slope, whilst the Stour Valley long barrows are constructed of earth.[23]

Agriculture and industry

Looking east across Denbies Wine Estate towards Box Hill near Dorking, Surrey.

The landscape of the Downs has been greatly shaped by man. There has been

Champagne
region.

There is plenty of evidence of chalk extraction on the Downs, particularly along the scarp slope. Oil has been drilled at the foot of the Downs in several locations in Surrey. The Kent Coalfield was established in the late 19th century after coal was found in 1890. Four successful collieries continued to be worked through much of the 20th century: Betteshanger, Snowdown, Tilmanstone and Chislet; Bettershanger was the last to close in 1989. The east to west ridge of the Downs has provided a natural transport route for centuries. Much of the historic Pilgrims' Way still survives at the foot of the scarp slope, and this has been joined much more recently by the M20 motorway. The scarp slope has also been used for fortification; many examples of this still exist, such as Thurnham Castle and on Castle Hill, Folkestone Castle Hill near Folkestone.

Places of interest

Many beauty spots on the North Downs are owned by the

Wye Downs and the Hog's Back. Much chalk grassland and ancient woodland on the Downs is open-access, and there are also many historic sites such as Kit's Coty House (near Maidstone) and Dover Castle
.

Hills

The topography of the North Downs means there are relatively few summits with topographic prominence. Below is a list of summits on the North Downs which are more than 180 metres in height with 30 metres of topographic prominence (a commonly used threshold in Britain). The summits are arranged in order along the range, from west to east.

Hill Height (m) Prominence (m) OS grid reference
Dunley Hill 227 105 TQ104490
Box Hill 224 53 TQ203517
Reigate Hill 235 100 TQ255520
White Hill 233 30 TQ328532
Gravelly Hill 237 64 TQ337532
Winders Hill 236 47 TQ353540
Botley Hill 270 209 TQ387551
Wrotham Hill 235 129 TQ593600
Detling Hill 200 163 TQ804586
West Down 186 73 TR091453
Tolsford Hill
 183 61 TR159386
Cheriton Hill 188 150 TR197396

Photo gallery

  • The North Downs at the Wye Downs National Nature Reserve
    The North Downs at the
    Wye Downs
    National Nature Reserve
  • The North Downs above Hollingbourne.
    The North Downs above Hollingbourne.
  • A marker on the North Downs Way, Ranscombe Farm, Cuxton, Kent
    A marker on the
    Ranscombe Farm, Cuxton, Kent
  • Bluebells at Ranscombe Farm
    Bluebells at Ranscombe Farm
  • Looking East, typical downland scenery in the Medway Gap, Ranscombe Farm
    Looking East, typical downland scenery in the Medway Gap, Ranscombe Farm
  • A dry valley on the dip slope of the North Downs near Hucking
    A dry valley on the dip slope of the North Downs near Hucking
  • Woodland on the North Downs at the Hucking Estate
    Woodland on the North Downs at the Hucking Estate
  • Typical chalk downland trail near Hollingbourne
    Typical chalk downland trail near Hollingbourne
  • A modern metal trail marker near Harrietsham
    A modern metal trail marker near Harrietsham
  • A view South across the Kent Weald from the North Downs Way near Detling
    A view South across the Kent Weald from the North Downs Way near Detling

See also

References

  1. ^ a b c d e "North Downs Natural Area profile" (PDF). English Nature. August 1997. Archived from the original (PDF) on 27 October 2015. Retrieved 12 September 2007.
  2. ^ "d | Origin and history of d by Online Etymology Dictionary". Etymonline.com. Archived from the original on 14 May 2011. Retrieved 16 September 2017.
  3. ^ The Mountains of England of Wales, Botley Hill, http://www.hill-bagging.co.uk/mountaindetails.php?qu=Ma&rf=3686 Archived 3 May 2014 at the Wayback Machine, Retrieved 4 March 2012
  4. ^ a b Bathurst 2012, pp. 82–82
  5. ^ Simon Edwardes (2001). "County Tops". The Mountains of England and Wales. Archived from the original on 3 May 2014. Retrieved 20 April 2014.
  6. ^ The Mountains of England and Wales, Westerham Heights, http://www.hill-bagging.co.uk/mountaindetails.php?qu=Ma&rf=5503 Archived 3 May 2014 at the Wayback Machine, Retrieved 4 March 2012
  7. ^ Gallois RW and Edmunds FH (1965) British Regional Geology: The Wealden District (4th Ed.) published by the Natural Environment Research Council: Institute of Geological Sciences
  8. ^ Bennison & Wright 1969, p. 321
  9. ^ Chapman & Young 1979, p. 26
  10. ^ a b Gallois, RW (2009). "The origin of the Clay-with-flints: the missing link". Geoscience in South-West England. 12: 153–161.
  11. ^ Anon. "Clay-with Flints formation". The BGS Lexicon of Named Rock Units. BGS. Archived from the original on 9 September 2017. Retrieved 3 May 2017.
  12. doi:10.1016/S0016-7878(75)80061-7
    .
  13. ISBN 0-11-884078-9
    .
  14. ^ Chapman & Young 1979, pp. 15–29
  15. doi:10.1111/j.1475-2743.1993.tb00919.x
    .
  16. ^ a b Lester, DE (2015). "Geomorphology of the Mole Valley" (PDF). Mole Valley Geological Society. Archived (PDF) from the original on 16 November 2017. Retrieved 17 July 2020.
  17. S2CID 129120488
    .
  18. doi:10.1016/S0016-7878(85)80011-0
    .
  19. ^ "What's special about chalk grassland?". National Trust. National Trust. Archived from the original on 25 October 2019. Retrieved 25 October 2019.
  20. ISBN 978-1-9015-0947-2. Archived from the original
    (PDF) on 13 September 2012.
  21. ^
    ISBN 1-86077-353-2
    .
  22. ^ "Britain's Orchids, Lady Orchid". Wild Guides and English Nature. Archived from the original on 3 March 2016. Retrieved 12 September 2007.
  23. ^
    ISBN 978-0-7524-4405-5
    .
  24. ^ "Prehistory and The Romans". Guildford Borough. Archived from the original on 22 December 2007. Retrieved 21 February 2008.

Bibliography

External links

Look up north downs in Wiktionary, the free dictionary.
Wikimedia Commons has media related to North Downs.

51°16′N 0°30′W / 51.267°N 0.500°W / 51.267; -0.500

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