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22-564: Downlands may refer to: Downland , an area of open chalk hills, especially in southern England Downlands College , a school in Queensland, Australia Downlands Community School in West Sussex, England Topics referred to by the same term [REDACTED] This disambiguation page lists articles associated with the title Downlands . If an internal link led you here, you may wish to change

44-540: A 20% loss in that period and an assessment of chalk grassland in Dorset found that over 50% had been lost between the mid-1950s and the early 1990s. Much remaining chalk downland has been protected against future development to preserve its unique biodiversity . Alpine Orogeny The Alpine orogeny or Alpide orogeny is an orogenic phase in the Late Mesozoic (Eoalpine) and the current Cenozoic that has formed

66-440: A chalk rendzina soil consists of only a shallow dark humus rich surface layer which grades through a lighter brown hillwash containing small pellets of chalk, to the white of the chalk itself. This is largely because of the purity of the chalk, which is about 98% calcium carbonate , and the consequent absence of soil-building clay minerals which are abundant, for example, in valley floors. Steep slopes on chalk downland develop

88-567: A much gentler dip slope on the other. Where the downs meet the sea, characteristic white chalk cliffs form, such as the White Cliffs of Dover and Beachy Head . Chalk deposits are generally very permeable, so the height of the water table in chalk hills rises in winter and falls in summer. This leads to characteristic chalk downland features such as dry valleys or coombes , and seasonally-flowing streams or winterbournes . The practice of extracting water from this aquifer, in order to satisfy

110-426: A ribbed pattern of grass covered horizontal steps a foot or two high. Although subsequently emphasised by cattle and sheep walking along them, these terracettes (commonly known as sheep tracks) were formed by the movement of soil downhill, a process known as soil creep . The dominant habitat in chalk downland is typically calcareous grassland , formed by grazing from both livestock and wild animals. Chalk downland

132-712: Is formed by Salisbury Plain , mainly in Wiltshire . To the southwest, downlands continue via Cranborne Chase into Dorset as the Dorset Downs and southwards through Hampshire as the Hampshire Downs onto the Isle of Wight . To the northeast, downlands continue along the Berkshire Downs and Chiltern Hills through parts of Berkshire , Oxfordshire , Buckinghamshire , Hertfordshire , Bedfordshire and into Cambridgeshire . To

154-487: Is often unsuitable for intensive agriculture , horticulture , or development because of the nutrient-poor, shallow soil and difficult slopes. For this reason downland often survived uncultivated when other, more easily worked land was ploughed or reseeded. This shallow soil structure makes downland ecosystems extremely fragile and easy to destroy. With modern machinery and fertilising techniques, it has become possible to use some previously uncultivated downland for farming, and

176-500: Is relatively soft porous white chalk with only poorly-defined bedding. The chalk is classified as a biomicrite , with microscopic coccoliths and other fine-grained fossil debris in a matrix of micrite mud. Small amounts of silica were also deposited, mainly from sponge spicules , which moved during diagenesis and accumulated to form flints . The Chalk Group either directly overlies the impermeable uppermost Lower Cretaceous Gault Clay or permeable Upper Greensand Formation above

198-1397: The Alps , the Apennine Mountains , the Dinaric Alps , the Accursed Mountains (Albanides), the Pindus (Hellenides), the Carpathians , the Balkanides (the Balkan Mountains and Rila - Rhodope massifs ), the Pontic Mountains , the Taurus , the Antitaurus , the Armenian Highlands , the Caucasus , the Alborz , the Zagros , the Hajar , the Hindu Kush , the Pamir , the Karakoram , and

220-741: The Himalayas . Sometimes other names occur to describe the formation of separate mountain ranges: for example Carpathian orogeny for the Carpathians , Hellenic orogeny for the Pindus , Altai orogeny for the Altai Mountains or the Himalayan orogeny for the Himalayas . The Alpine orogeny has also led to the formation of more distant and smaller geological features such as the Weald–Artois Anticline in Southern England and northern France,

242-865: The Old Red Sandstone Continent when the continents Baltica and Laurentia collided in the early Paleozoic , and the Hercynian or Variscan orogeny that formed Pangaea when Gondwana and the Old Red Sandstone Continent collided in the middle to late Paleozoic. These mountains include (from west to east) the Atlas , the Rif , the Baetic Cordillera , the Cantabrian Mountains , the Pyrenees ,

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264-637: The Gault Clay. Since its deposition, the chalk in southern England has been uplifted, faulted , fractured and folded by the distant effects of the Alpine Orogeny . The fracturing has greatly increased the chalk's permeability, such that it is a major aquifer . Sedimentary basins formed by rifting during the Triassic to Early Cretaceous were inverted during the Late Paleogene to Miocene leading to

286-468: The chalk and the modification of existing valleys due to a combination of frozen ground and snowmelt . Downland develops when chalk rock becomes exposed at the surface. The chalk slowly erodes to form characteristic rolling hills and valleys. As the Cretaceous chalk layer in southern England is typically tilted, chalk downland hills often have a marked scarp slope on one side, which is very steep, and

308-491: The decline of extensive grazing has meant that many areas of downland, neither cultivated nor grazed, revert to scrub or other less rare habitat, essentially destroying the delicate calcareous grassland. The UK cover of lowland calcareous grassland has suffered a sharp decline in extent since the middle of the twentieth century. There are no comprehensive figures, but a sample of chalk sites in England surveyed in 1966 and 1980 showed

330-742: The east downlands are found north of the Weald in Surrey , Kent and part of Greater London , forming the North Downs . To the southeast the downlands continue into West Sussex and East Sussex as the South Downs . Similar chalk hills are also found further north in Lincolnshire and Yorkshire where they are known as the Wolds . The Chalk Group is a sequence of Upper Cretaceous limestones . The dominant lithology

352-591: The formation of structures such as the Wealden Anticline and the Portland-Wight Monocline . Later erosion has produced the characteristic ridges of the downland landscape. The landscape was further modified during the Quaternary period by the area's proximity to the southern edge of the ice sheets formed during the last ice age . These periglacial effects included significant amounts of dissolution of

374-423: The increasing demand for water, may be putting some of these streams under stress. In the valleys below the downs at the base of the chalk layer, greensand or gault clay comes to the surface and at the interface at the top of the gault a springline can occur where water emerges from the porous chalk or the underlying greensand. Along this line, settlements and farms were often built, as on the higher land no water

396-407: The link to point directly to the intended article. Retrieved from " https://en.wikipedia.org/w/index.php?title=Downlands&oldid=585065398 " Category : Disambiguation pages Hidden categories: Short description is different from Wikidata All article disambiguation pages All disambiguation pages Downland The largest area of downland in southern England

418-729: The mountain ranges of the Alpide belt . The Alpine orogeny is caused by the continents Africa , Arabia and India and the small Cimmerian Plate colliding (from the south) with Eurasia in the north. Convergent movements between the tectonic plates (the African Plate , the Arabian Plate and the Indian Plate from the south, the Eurasian Plate and the Anatolian Sub-Plate from

440-624: The north, and many smaller plates and microplates) had already begun in the early Cretaceous , but the major phases of mountain building began in the Paleocene to Eocene. The process continues currently in some of the Alpide mountain ranges. The Alpine orogeny is considered one of the three major phases of orogeny in Europe that define the geology of that continent, along with the Caledonian orogeny that formed

462-553: The remains of which can be seen in the chalk ridges of the North and South Downs in southern England. Its effects are particularly visible on the Isle of Wight , where the Chalk Group and overlying Eocene strata are folded to near-vertical, as seen in exposures at Alum Bay and Whitecliff Bay , and on the Dorset coast near Lulworth Cove . Stresses arising from the Alpine orogeny caused

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484-603: Was available. This is demonstrated very clearly beneath the scarp of the White Horse Hills , above the Vale of White Horse . In many chalk downland areas there is no surface water at all other than artificially created dewponds . The soil profile of chalk downland in England is a thin soil overlaying the parent chalk . Weathering of the chalk has created a characteristic soil known as rendzina . Unlike many soils in which there are easily distinguished layers or soil horizons ,

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