Misplaced Pages

#634365

62-746: The North Downs are a ridge of chalk hills in south east England that stretch from Farnham in Surrey to the White Cliffs of Dover in Kent . Much of the North Downs comprises two Areas of Outstanding Natural Beauty (AONBs): the Surrey Hills and the Kent Downs . The North Downs Way National Trail runs along the North Downs from Farnham to Dover . The highest point in the North Downs

124-440: 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

186-468: A few are more recent. A mixture of chalk and mercury can be used as fingerprint powder . However, because of the toxicity of the mercury, the use of such mixtures for fingerprinting was abandoned in 1967. Downland The largest area of downland in southern England is formed by Salisbury Plain , mainly in Wiltshire . To the southwest, downlands continue via Cranborne Chase into Dorset as

248-538: A landscape similar to that found in Normandy known as bocage . The predominant type of farming on the Downs is arable farming; this increased greatly during the 20th century. Pastoral farming also occurs but to a lesser extent. Human settlements within the Downs have generally formed in sheltered valleys and at the foot of the scarp slope (known as spring line settlements). In recent years vineyards have been planted along

310-466: A mix of rubble and viscous mud, which may be washed downhill, further eroding the landscape (a process known as solifluction ). Since chalk contains a very high percentage of calcium carbonate , it can be dissolved by both groundwater and rainwater. 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

372-513: 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

434-426: 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

496-463: Is Botley Hill , Surrey (270 m (890 ft) above sea level). The County Top of Kent is Betsom's Hill (251 m (823 ft) above sea level), which is less than 1 km from Westerham Heights , Bromley , the highest point in Greater London at an elevation of 245 m (804 ft). 'Downs' is from Old English dun , meaning, amongst other things, "hill". The word acquired

558-642: Is mined from chalk deposits both above ground and underground . Chalk mining boomed during the Industrial Revolution , due to the need for chalk products such as quicklime and bricks . Most people first encounter chalk in school where it refers to blackboard chalk , which was originally made of mineral chalk, since it readily crumbles and leaves particles that stick loosely to rough surfaces, allowing it to make writing that can be readily erased. Blackboard chalk manufacturers now may use mineral chalk, other mineral sources of calcium carbonate, or

620-610: Is a fine-textured, earthy type of limestone distinguished by its light colour, softness, and high porosity. It is composed mostly of tiny fragments of the calcite shells or skeletons of plankton , such as foraminifera or coccolithophores . These fragments mostly take the form of calcite plates ranging from 0.5 to 4 microns in size, though about 10% to 25% of a typical chalk is composed of fragments that are 10 to 100 microns in size. The larger fragments include intact plankton skeletons and skeletal fragments of larger organisms, such as molluscs , echinoderms , or bryozoans . Chalk

682-516: Is absent. The alkaline soils are thin and nutrient poor, which prevents deeper-rooted lush grasses (with a high water demand) from dominating. Each square metre of chalk downland may support up to 40 different species. This semi-natural habitat is maintained through sheep, cattle and rabbit grazing which prevents scrub encroachment. Chalk grassland to the west of the Medway Valley is dominated by upright brome and fescue , whilst grassland to

SECTION 10

#1732765551635

744-508: Is also the only form of limestone that commonly shows signs of compaction. Flint (a type of chert ) is very common as bands parallel to the bedding or as nodules in seams , or linings to fractures , embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint). Chalk

806-428: Is applied to the hands and feet to remove perspiration and reduce slipping. Chalk may also be used as a house construction material instead of brick or wattle and daub : quarried chalk was cut into blocks and used as ashlar , or loose chalk was rammed into blocks and laid in mortar. There are still houses standing which have been constructed using chalk as the main building material. Most are pre- Victorian though

868-418: 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

930-690: Is common throughout Western Europe , where deposits underlie parts of France, and steep cliffs are often seen where they meet the sea in places such as the Dover cliffs on the Kent coast of the English Channel . Chalk is mined for use in industry, such as for quicklime , bricks and builder's putty , and in agriculture , for raising pH in soils with high acidity . It is also used for " blackboard chalk " for writing and drawing on various types of surfaces, although these can also be manufactured from other carbonate-based minerals, or gypsum . Chalk

992-518: Is commonly used as a drying agent to obtain better grip by gymnasts and rock climbers. Glazing putty mainly contains chalk as a filler in linseed oil . Chalk and other forms of limestone may be used for their properties as a base . Chalk is a source of quicklime by thermal decomposition , or slaked lime following quenching of quicklime with water. In agriculture , chalk is used for raising pH in soils with high acidity . Small doses of chalk can also be used as an antacid . Additionally,

1054-523: Is considerable evidence of Mesolithic activity in the Surrey Downs through the discovery of pit-dwellings at Weston Woods near Albury and the quantity of discarded tools, microliths and other implements discovered. In about 3000 BC the emergence of Neolithic culture saw the lifestyle of the Mesolithic hunter-gatherers shift to a more sedentary and communal lifestyle that relied upon

1116-582: Is now usually made of talc (magnesium silicate). Chalk beds form important petroleum reservoirs in the North Sea and along the Gulf Coast of North America. In southeast England, deneholes are a notable example of ancient chalk pits. Such bell pits may also mark the sites of ancient flint mines, where the prime object was to remove flint nodules for stone tool manufacture. The surface remains at Cissbury are one such example, but perhaps

1178-487: 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

1240-554: Is so common in Cretaceous marine beds that the Cretaceous Period was named for these deposits. The name Cretaceous was derived from Latin creta , meaning chalk . Some deposits of chalk were formed after the Cretaceous. The Chalk Group is a European stratigraphic unit deposited during the late Cretaceous Period. It forms the famous White Cliffs of Dover in Kent , England, as well as their counterparts of

1302-401: Is typically almost pure calcite, CaCO 3 , with just 2% to 4% of other minerals. These are usually quartz and clay minerals , though collophane (cryptocrystalline apatite , a phosphate mineral) is also sometimes present, as nodules or as small pellets interpreted as fecal pellets. In some chalk beds, the calcite has been converted to dolomite , CaMg(CO 3 ) 2 , and in a few cases

SECTION 20

#1732765551635

1364-752: The Cap Blanc Nez on the other side of the Dover Strait . The Champagne region of France is mostly underlain by chalk deposits, which contain artificial caves used for wine storage . Some of the highest chalk cliffs in the world occur at Jasmund National Park in Germany and at Møns Klint in Denmark . Chalk deposits are also found in Cretaceous beds on other continents, such as the Austin Chalk , Selma Group , and Niobrara Formations of

1426-714: 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 the east downlands are found north of the Weald in Surrey , Kent and part of Greater London , forming

1488-608: 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 . 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

1550-643: 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 is relatively soft porous white chalk with only poorly-defined bedding. The chalk

1612-520: 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 the same geological processes that created the Alps , resulting in an anticline which stretched across the English Channel to the Artois region of northern France. Initially an island, this dome-like structure

1674-416: The Downs has been greatly shaped by man. There has been deforestation of the Downs for centuries. The woodland that remains today is largely located where deforestation has been inhibited by steep slopes or by the layer of clay with flints, which is difficult to plough. Because of the many small farms that have survived on the Downs, a network of narrow lanes and minor roads has developed. This has resulted in

1736-662: 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

1798-575: 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 Botley Hill in Surrey at 269 m (883 ft). The County top of Kent at Betsom's Hill , with a height of 251 m (823 ft), is nearby, and the highest point in Greater London , Westerham Heights , at 245 m (804 ft), is on

1860-732: The North American interior. Chalk is also found in western Egypt (Khoman Formation) and western Australia ( Miria Formation ). Chalk of Oligocene to Neogene age has been found in drill cores of rock under the Pacific Ocean at Stewart Arch in the Solomon Islands . There are layers of chalk, containing Globorotalia , in the Nicosia Formation of Cyprus , which formed during the Pliocene . Chalk

1922-465: The Stour Valley is the only British site for the black-veined moth . Other notable moth species that occur on the North Downs include the fiery clearwing moth and the straw belle moth . On the summit of the cliffs between Deal and Folkestone the early spider orchid occurs in large numbers, as well as the rare oxtongue broomrape . Naturally exposed chalk is rare inland with the exception of

North Downs - Misplaced Pages Continue

1984-569: The UK. 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 . 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

2046-611: 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 and does not consist of chalk. The Downland of the North Downs consists of distinct lithostratigraphic units (the types of strata, the names of which are always capitalised): Following

2108-485: 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. Worked flints and human and animal remains dating from the Lower Paleolithic , about 400,000 years ago, were discovered at Barnfield Pit near Swanscombe ; this provides

2170-446: The chalk and provide natural corridor routes. In addition to existing rivers, the Downs are crossed by a number of wind gaps – prehistoric river valleys no longer occupied by rivers – including those at Farnham , 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

2232-474: 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

2294-548: The chalk came mostly form low-magnesium calcite skeletons, so the sediments were already in the form of highly stable low-magnesium calcite when deposited. This is in contrast with most other limestones, which formed from high-magnesium calcite or aragonite that rapidly converted to the more stable low-magnesium calcite after deposition, resulting in the early cementation of such limestones. In chalk, absence of this calcium carbonate conversion process prevented early cementation, which partially accounts for chalk's high porosity. Chalk

2356-496: 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

2418-494: The dolomitized chalk has been dedolomitized back to calcite. Chalk is highly porous, with typical values of porosity ranging from 35 to 47 per cent. While it is similar in appearance to both gypsum and diatomite , chalk is identifiable by its hardness, fossil content, and its reaction to acid (it produces effervescence on contact). In Western Europe, chalk was formed in the Late Cretaceous Epoch and

2480-430: The earliest evidence of human occupation in the North Downs. It is suggested that human activity at that time coincided with intermittent warm phases during the last glacial period and that continuous occupation of the Downs did not occur until warming after the glaciation. Flint axes have also been found on river terraces at Farnham, on Walton and Banstead Heaths and on the crest of the escarpment above Folkestone. There

2542-437: The early Palaeocene Epoch (between 100 and 61 million years ago). It was deposited on extensive continental shelves at depths between 100 and 600 metres (330 and 1,970 ft), during a time of nonseasonal (likely arid) climate that reduced the amount of erosion from nearby exposed rock. The lack of nearby erosion explains the high purity of chalk. The coccolithophores, foraminifera, and other microscopic organisms from which

North Downs - Misplaced Pages Continue

2604-533: The east is dominated by tor-grass . 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

2666-563: 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. Many beauty spots on the North Downs are owned by the National Trust , for instance Box Hill and Langdon Cliffs . Other areas of interest are Newland's Corner , Wye Downs and

2728-557: 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

2790-423: 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

2852-524: The keeping of livestock and the growing of crops. There is substantial evidence of Neolithic activity within the North Downs, notably the long barrows concentrated in the Medway and Stour valleys. The Medway long barrows , which include Kit's Coty House and 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. The landscape of

2914-424: The layer of clay-with-flints overlying the chalk has inhibited clearance. Where this is the case species such as pedunculate oak predominate, although much woodland has been replanted with conifer and sweet chestnut . 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

2976-528: The mineral gypsum ( calcium sulfate ). While gypsum-based blackboard chalk is the lowest cost to produce, and thus widely used in the developing world , use of carbonate-based chalk produces larger particles and thus less dust, and it is marketed as "dustless chalk". Coloured chalks, pastel chalks, and sidewalk chalk (shaped into larger sticks and often coloured), used to draw on sidewalks , streets, and driveways , are primarily made of gypsum rather than calcium carbonate chalk. Magnesium carbonate chalk

3038-562: The most famous is the extensive complex at Grimes Graves in Norfolk . Chalk was traditionally used in recreation. In field sports, such as tennis played on grass, powdered chalk was used to mark the boundary lines of the playing field or court. If a ball hits the line, a cloud of chalk or pigment dust will be visible. In recent years, powdered chalk has been replaced with titanium dioxide . In gymnastics, rock-climbing, weightlifting and tug of war , chalk — now usually magnesium carbonate —

3100-566: The northern side of the same hill. East of the 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 Wey , Mole , Darent , Medway and Stour . These drain much of the Weald to the south. The western rivers are tributaries of the Thames ; they have carved steep valleys through

3162-415: 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

SECTION 50

#1732765551635

3224-403: The range, from west to east. 51°16′N 0°30′W  /  51.267°N 0.500°W  / 51.267; -0.500 Chalk Chalk is a soft, white, porous , sedimentary carbonate rock . It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor . Chalk

3286-401: The range, local faulting has produced a much steeper angle (up to 55°), resulting in the distinctive Hog's Back between Farnham and Guildford. The North Downs support several important habitats including chalk grassland , scrub , woodland and chalk heath . Chalk grassland is found on the steep south-facing scarp slopes and the more gently graded north-facing dip slopes, where woodland

3348-440: The ridge in the east. The North Downs cuesta has a steep south-facing scarp slope and a more gentle north-facing dip slope . Its southern boundary is defined by the low-lying 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. The Downs are highest near

3410-540: The river cliffs formed by the River Mole on the west face of Box Hill and at Ham Bank in Norbury Park . However, quarry lakes within chalk pits provide habitats for great crested newt . The scarce musk orchid has colonised disused chalk pits near Hollingbourne in Kent. Woodland was far more extensive on the North Downs prior to human clearance 5000 to 4000 years ago. Fragments still remain particularly where

3472-426: The sense of "elevated rolling grassland" around the 14th century. 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. The narrow spine of the Hog's Back between Farnham and Guildford forms the western extremity of the North Downs, whilst the cliffs between Folkestone and Deal terminate

3534-436: The small particles of chalk make it a substance ideal for cleaning and polishing. For example, toothpaste commonly contains small amounts of chalk, which serves as a mild abrasive . Polishing chalk is chalk prepared with a carefully controlled grain size, for very fine polishing of metals. French chalk (also known as tailor's chalk) is traditionally a hard chalk used to make temporary markings on cloth, mainly by tailors . It

3596-563: The southern slopes of the Downs, in particular the Denbies Wine Estate , Dorking , which is the largest vineyard in the country, accounting for 10% of the country's vines. The chalky soils are similar to those of the 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

3658-569: 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. Chalk grassland also supports a rich fauna, particularly insects. Notable butterfly species include Adonis blue and silver-spotted skipper , which may be found on warm, sheltered, south-facing slopes. The chalk downland above

3720-615: 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 ,

3782-658: 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. 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, and is therefore highly susceptible to weathering by freeze-thaw action , which may occur over repeated annual or diurnal cycles. This frost weathering produces

SECTION 60

#1732765551635

3844-401: 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

#634365