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104-506: Burrator Reservoir is a reservoir situated on the southern side of Dartmoor in Devon , England. It is part of a number of reservoirs and dams that were built over the course of the 19th and 20th centuries in the area now covered by Dartmoor National Park to supply drinking water to the city of Plymouth and other rapidly growing towns in the surrounding lowlands. Burrator Reservoir was completed in 1898 and later expanded in 1929. The reservoir

208-553: A basaltic magma to a granitic magma, but the quantities produced are small. For example, granitic rock makes up just 4% of the exposures in the South Sandwich Islands . In continental arc settings, granitic rocks are the most common plutonic rocks, and batholiths composed of these rock types extend the entire length of the arc. There are no indication of magma chambers where basaltic magmas differentiate into granites, or of cumulates produced by mafic crystals settling out of

312-520: A diapir it would expend far too much energy in heating wall rocks, thus cooling and solidifying before reaching higher levels within the crust. Fracture propagation is the mechanism preferred by many geologists as it largely eliminates the major problems of moving a huge mass of magma through cold brittle crust. Magma rises instead in small channels along self-propagating dykes which form along new or pre-existing fracture or fault systems and networks of active shear zones. As these narrow conduits open,

416-610: A granite that is derived from partial melting of metasedimentary rocks may have more alkali feldspar, whereas a granite derived from partial melting of metaigneous rocks may be richer in plagioclase. It is on this basis that the modern "alphabet" classification schemes are based. The letter-based Chappell & White classification system was proposed initially to divide granites into I-type (igneous source) granite and S-type (sedimentary sources). Both types are produced by partial melting of crustal rocks, either metaigneous rocks or metasedimentary rocks. I-type granites are characterized by

520-565: A high content of sodium and calcium, and by a strontium isotope ratio, Sr/ Sr, of less than 0.708. Sr is produced by radioactive decay of Rb, and since rubidium is concentrated in the crust relative to the mantle, a low ratio suggests origin in the mantle. The elevated sodium and calcium favor crystallization of hornblende rather than biotite. I-type granites are known for their porphyry copper deposits. I-type granites are orogenic (associated with mountain building) and usually metaluminous. S-type granites are sodium-poor and aluminum-rich. As

624-503: A more complete list see List of Dartmoor tors and hills . The high ground of Dartmoor forms the catchment area for many of Devon's rivers. As well as shaping the landscape, these have traditionally provided a source of power for moor industries such as tin mining and quarrying. The moor takes its name from the River Dart , which starts as the East Dart and West Dart and then becomes

728-820: A much higher proportion of clay with the Cecil soil series a prime example of the consequent Ultisol great soil group. Granite is a natural source of radiation , like most natural stones. Potassium-40 is a radioactive isotope of weak emission, and a constituent of alkali feldspar , which in turn is a common component of granitic rocks, more abundant in alkali feldspar granite and syenites . Some granites contain around 10 to 20 parts per million (ppm) of uranium . By contrast, more mafic rocks, such as tonalite, gabbro and diorite , have 1 to 5 ppm uranium, and limestones and sedimentary rocks usually have equally low amounts. Many large granite plutons are sources for palaeochannel -hosted or roll front uranium ore deposits , where

832-543: A mysterious pack of " spectral hounds ", and a large black dog , among others. During the Great Thunderstorm of 1638, the moorland village of Widecombe-in-the-Moor was said to have been visited by the Devil . Granite Granite is typical of a larger family of granitic rocks , or granitoids , that are composed mostly of coarse-grained quartz and feldspars in varying proportions. These rocks are classified by

936-650: A number do not. However, this does not appear to relate to whether or not there is an outcrop of rock on their summit. The tors are the focus of an annual event known as the Ten Tors Challenge , when around 2,400 people aged between 14 and 19 walk for distances of 56, 72 or 88 km (35, 45 or 55 mi) between ten tors on many differing routes. The highest points on Dartmoor are on the northern moor: High Willhays , 621 m (2,037 ft), ( grid reference SX 580892 ) and Yes Tor , 619 m (2,031 ft), ( grid reference SX 581901 ). The highest points on

1040-474: A number of migrant species, like the pied flycatcher , the wood warbler or the common redstart . Mammals found here include otters, hazel dormice and nearly all of the UK's 16 bat species. Three rare species: the barbastelle , and the greater and lesser horseshoe bats are of particular importance. The upper reaches of the rivers are spawning grounds for Salmon and trout ; Palmate newts , frogs and toads breed in

1144-536: A peculiar mineralogy and geochemistry, with particularly high silicon and potassium at the expense of calcium and magnesium and a high content of high field strength cations (cations with a small radius and high electrical charge, such as zirconium , niobium , tantalum , and rare earth elements .) They are not orogenic, forming instead over hot spots and continental rifting, and are metaluminous to mildly peralkaline and iron-rich. These granites are produced by partial melting of refractory lithology such as granulites in

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1248-472: A person's feet. Quakers result from sphagnum moss growing over the water that accumulates in the hollows in the granite. The vegetation of the bogs depends on the type and location. Blanket bog , which forms on the highest land where the rainfall exceeds 2,000 millimetres (79 in) a year, consists mainly of cotton-grass ( Eriophorum species), sedges ( Carex and Rhynchospora ), Bog Asphodel and Common Tormentil , with Sphagnum thriving in

1352-568: A range of hills, formed by the metamorphic aureole or hornfels . Granite often occurs as relatively small, less than 100 km stock masses ( stocks ) and in batholiths that are often associated with orogenic mountain ranges. Small dikes of granitic composition called aplites are often associated with the margins of granitic intrusions . In some locations, very coarse-grained pegmatite masses occur with granite. Granite forms from silica-rich ( felsic ) magmas. Felsic magmas are thought to form by addition of heat or water vapor to rock of

1456-415: A result, they contain micas such as biotite and muscovite instead of hornblende. Their strontium isotope ratio is typically greater than 0.708, suggesting a crustal origin. They also commonly contain xenoliths of metamorphosed sedimentary rock, and host tin ores. Their magmas are water-rich, and they readily solidify as the water outgasses from the magma at lower pressure, so they less commonly make it to

1560-881: A single river at Dartmeet . It leaves the moor at Buckfastleigh , flowing through Totnes below where it opens up into a long ria , reaching the sea at Dartmouth . Other rivers flowing from Dartmoor include the Teign , the Taw , the Tavy , the Avon , and the Lyd . Some of the rivers in Dartmoor have been dammed to create reservoirs for drinking water , including the River Avon and the South Teign River (Fernworthy Reservoir). Much more rain falls on Dartmoor than in

1664-437: A species found nowhere else in the world. The South West Peatland Project aims to restore around 300 hectares of Dartmoor's peatland through collaboration with Dartmoor National Park . Preserving these peatlands will help mitigate climate change through sequestering carbon from the atmosphere. More generally, Dartmoor aims to be carbon negative by 2045. The majority of the prehistoric remains on Dartmoor date back to

1768-466: Is grus , which is often made up of coarse-grained fragments of disintegrated granite. Climatic variations also influence the weathering rate of granites. For about two thousand years, the relief engravings on Cleopatra's Needle obelisk had survived the arid conditions of its origin before its transfer to London. Within two hundred years, the red granite has drastically deteriorated in the damp and polluted air there. Soil development on granite reflects

1872-539: Is microgranite . The extrusive igneous rock equivalent of granite is rhyolite . Granitic rock is widely distributed throughout the continental crust . Much of it was intruded during the Precambrian age; it is the most abundant basement rock that underlies the relatively thin sedimentary veneer of the continents. Outcrops of granite tend to form tors , domes or bornhardts , and rounded massifs . Granites sometimes occur in circular depressions surrounded by

1976-517: Is 3–6·10 Pa·s. The melting temperature of dry granite at ambient pressure is 1215–1260 °C (2219–2300 °F); it is strongly reduced in the presence of water, down to 650 °C at a few hundred megapascals of pressure. Granite has poor primary permeability overall, but strong secondary permeability through cracks and fractures if they are present. A worldwide average of the chemical composition of granite, by weight percent, based on 2485 analyses: The medium-grained equivalent of granite

2080-549: Is about 150 acres. The reservoir's edges are planted with commercial forests. Today, Burrator Reservoir is managed by the South West Lakes Trust and serves as a popular destination for leisure activities such as walking, cycling, and fishing. The reservoir featured in the first episode of the second series of James May's Man Lab , broadcast on BBC Two in October 2011, when Oz Clarke and James May travelled along

2184-410: Is an excess of aluminum beyond what can be taken up in feldspars (Al 2 O 3 > CaO + K 2 O + Na 2 O) are described as peraluminous , and they contain aluminum-rich minerals such as muscovite . The average density of granite is between 2.65 and 2.75 g/cm (165 and 172 lb/cu ft), its compressive strength usually lies above 200 MPa (29,000 psi), and its viscosity near STP

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2288-419: Is associated with the Dartmoor pluton as with other such plutons . Measurement of the anomaly has helped to determine the likely shape and extent of the rock mass at depth. Dartmoor is known for its tors – hills topped with outcrops of bedrock, which in granite country such as this are usually rounded boulder-like formations. More than 160 of the hills of Dartmoor have the word tor in their name but quite

2392-524: Is at least five times as frequent. On the highest ground, in the north of the moor, the growing season is less than 175 days – this contrasts with some 300 days along most of the south coast of the county. Rainfall tends to be associated with Atlantic depressions or with convection. In summer, convection caused by solar surface heating sometimes forms shower clouds and a large proportion of rainfall comes from showers and thunderstorms at this time of year. The wettest months are November and December and on

2496-430: Is believed that they would have had a conical roof, supported by timbers and covered in turf or thatch. There are also numerous kistvaens , Neolithic stone box-like tombs. The climate became wetter and cooler over the course of a thousand years from around 1000 BC, resulting in much of high Dartmoor being largely abandoned by its early inhabitants. The earliest surviving farms, still in operation today, are known as

2600-618: Is believed to have a mass of around 81 tonnes. It was the tallest temple in south India. Imperial Roman granite was quarried mainly in Egypt, and also in Turkey, and on the islands of Elba and Giglio . Granite became "an integral part of the Roman language of monumental architecture". The quarrying ceased around the third century AD. Beginning in Late Antiquity the granite was reused, which since at least

2704-434: Is called a binary or two-mica granite. Two-mica granites are typically high in potassium and low in plagioclase, and are usually S-type granites or A-type granites, as described below . Another aspect of granite classification is the ratios of metals that potentially form feldspars. Most granites have a composition such that almost all their aluminum and alkali metals (sodium and potassium) are combined as feldspar. This

2808-462: Is granted extensive land access rights on Dartmoor (including restricted access to the firing ranges) and it is a popular tourist destination. Dartmoor includes the largest area of granite in Britain, with about 625 km (241 sq mi) at the surface, though most of it is under superficial peat deposits. The granite (or more specifically adamellite ) was intruded at depth as a pluton into

2912-433: Is limited by the amount of thermal energy available, which must be replenished by crystallization of higher-melting minerals in the magma. Thus, the magma is melting crustal rock at its roof while simultaneously crystallizing at its base. This results in steady contamination with crustal material as the magma rises. This may not be evident in the major and minor element chemistry, since the minerals most likely to crystallize at

3016-404: Is permeated by sheets and channels of light granitic rock (the leucosome ). The leucosome is interpreted as partial melt of a parent rock that has begun to separate from the remaining solid residue (the melanosome). If enough partial melt is produced, it will separate from the source rock, become more highly evolved through fractional crystallization during its ascent toward the surface, and become

3120-603: Is possibly a surviving fragment from the earliest Neolithic woodland clearances. It is home to exceptional epiphytic mosses, liverworts and lichens. Nearly 50 species of moss and liverwort are found in the wood along with 120 types of lichen , including Smith's horsehair lichen, speckled sea-storm lichen and pendulous wing-moss. Over 60 species of lichens grow on the exposed surfaces of the granite tors, including granite-speck rim-lichen, purple rock lichen, brown cobblestone lichen and goldspot lichen and many rare lichen grow on rocks exposed by mining that are rich in heavy metals . On

3224-454: Is relieved when overlying material is removed by erosion or other processes. Chemical weathering of granite occurs when dilute carbonic acid , and other acids present in rain and soil waters, alter feldspar in a process called hydrolysis . As demonstrated in the following reaction, this causes potassium feldspar to form kaolinite , with potassium ions, bicarbonate, and silica in solution as byproducts. An end product of granite weathering

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3328-450: Is remote from many sources of light pollution . However, in recent years, LED street lights have caused more light pollution to be spread onto Dartmoor. Along with the rest of South West England , Dartmoor has a temperate climate , which is generally wetter and milder than locations at similar height in the rest of England. At Princetown , near the centre of the moor at a height of 453 metres (1,486 ft), January and February are

3432-411: Is some concern that some granite sold as countertops or building material may be hazardous to health. Dan Steck of St. Johns University has stated that approximately 5% of all granite is of concern, with the caveat that only a tiny percentage of the tens of thousands of granite slab types have been tested. Resources from national geological survey organizations are accessible online to assist in assessing

3536-479: Is that magma will rise through the crust as a single mass through buoyancy . As it rises, it heats the wall rocks , causing them to behave as a power-law fluid and thus flow around the intrusion allowing it to pass without major heat loss. This is entirely feasible in the warm, ductile lower crust where rocks are easily deformed, but runs into problems in the upper crust which is far colder and more brittle. Rocks there do not deform so easily: for magma to rise as

3640-410: Is the case when K 2 O + Na 2 O + CaO > Al 2 O 3 > K 2 O + Na 2 O. Such granites are described as normal or metaluminous . Granites in which there is not enough aluminum to combine with all the alkali oxides as feldspar (Al 2 O 3 < K 2 O + Na 2 O) are described as peralkaline , and they contain unusual sodium amphiboles such as riebeckite . Granites in which there

3744-429: Is the more massive of the two dams, constructed of concrete faced with granite blocks. The Sheepstor Dam was built in 1894 and is an earth embankment with a core wall of puddled clay above the original ground level, with a concrete section below ground. The reservoir was officially opened on 21 September 1898. In 1923 plans were made to enlarge the reservoir's capacity from 668 million gallons to 1,026 million by raising

3848-455: Is typically orthoclase or microcline and is often perthitic . The plagioclase is typically sodium-rich oligoclase . Phenocrysts are usually alkali feldspar. Granitic rocks are classified according to the QAPF diagram for coarse grained plutonic rocks and are named according to the percentage of quartz , alkali feldspar ( orthoclase , sanidine , or microcline ) and plagioclase feldspar on

3952-428: Is uncommon, is classified simply as quartz-rich granitoid or, if composed almost entirely of quartz, as quartzolite . True granites are further classified by the percentage of their total feldspar that is alkali feldspar. Granites whose feldspar is 65% to 90% alkali feldspar are syenogranites , while the feldspar in monzogranite is 35% to 65% alkali feldspar. A granite containing both muscovite and biotite micas

4056-495: The Ancient Tenements . Most of these date back to the 14th century, and some even earlier. It was not until the early Mediaeval period that the weather again became warmer, and settlers moved back onto the moors. Like their ancient predecessors, they used the natural granite to build their homes, preferring a style known as the longhouse ; some of theses are still inhabited today, although they have been clearly adapted over

4160-474: The Dartmoor Commons Act 1985 much of it has been designated as access land , which, although it remains privately owned, has no restrictions on where walkers can roam. In addition to this access land, there are about 730 km (450 mi) of public rights of way on Dartmoor, and many kilometres of permitted footpaths and bridleways where the owners allow access. Because of the 1985 Act, Dartmoor

4264-427: The marsh fritillary butterfly, southern damselfly, narrow-bordered bee hawkmoth and bog hoverfly . Areas of bracken are home to the high brown fritillary and pearl-bordered fritillary . Insects found in the heathlands include the emperor moth , green hairstreak and the bilberry bumblebee . The old oak woodlands have a distinctive group of insects including the blue ground beetle and Heckford's pygmy moth ,

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4368-479: The moors topped with granite tors are the most iconic part of Dartmoor's landscape, only about half of Dartmoor is actually moorland. Equally important for wildlife are the blanket bogs , upland heaths and the oak woodlands, which are all of global importance. Dartmoor is a Special Area of Conservation (SAC) with four habitats ( Northern Atlantic wet heaths with Erica tetralix ; European dry heaths ; Blanket bog s and Old sessile oak woods with Ilex and Blechnum in

4472-567: The A-Q-P half of the diagram. True granite (according to modern petrologic convention) contains between 20% and 60% quartz by volume, with 35% to 90% of the total feldspar consisting of alkali feldspar . Granitic rocks poorer in quartz are classified as syenites or monzonites , while granitic rocks dominated by plagioclase are classified as granodiorites or tonalites . Granitic rocks with over 90% alkali feldspar are classified as alkali feldspar granites . Granitic rock with more than 60% quartz, which

4576-457: The British Isles ) being listed as primary reasons for the selection of Dartmoor as a SAC. In addition the area has a population of the southern damselfly , which is also a primary reason for its selection along with populations of Atlantic salmon and otter being qualifying reasons. Wistman's Wood is one of the old sessile oak woods that contribute to the listing of Dartmoor as a SAC and

4680-598: The European Union safety standards (section 4.1.1.1 of the National Health and Engineering study) and radon emission levels well below the average outdoor radon concentrations in the US. Granite and related marble industries are considered one of the oldest industries in the world, existing as far back as Ancient Egypt . Major modern exporters of granite include China, India, Italy, Brazil, Canada, Germany, Sweden, Spain and

4784-513: The MoD does not notify the public of this in advance. Some "challenge" and charitable events take place with assistance of the military on Dartmoor, including the long established Ten Tors event and the more recent Dartmoor Beast. The disused Rippon Tor Rifle Range was built to train soldiers during the Second World War, and remained in use until its closure in 1977. Throughout human history,

4888-631: The Mohs hardness scale) , and tough. These properties have made granite a widespread construction stone throughout human history. The word "granite" comes from the Latin granum , a grain, in reference to the coarse-grained structure of such a completely crystalline rock. Granitic rocks mainly consist of feldspar , quartz , mica , and amphibole minerals , which form an interlocking, somewhat equigranular matrix of feldspar and quartz with scattered darker biotite mica and amphibole (often hornblende ) peppering

4992-524: The National Park are Ashburton (the largest, with a population of about 3,500), Buckfastleigh , Moretonhampstead , Princetown , Yelverton , Horrabridge , South Brent , Christow , and Chagford . For a full list, expand the Settlements of Dartmoor navigational box at the bottom of this page. Dartmoor is known for its myths and legends. It is reputedly the haunt of pixies , a headless horseman ,

5096-504: The United States. The Red Pyramid of Egypt ( c.  2590 BC ), named for the light crimson hue of its exposed limestone surfaces, is the third largest of Egyptian pyramids . Pyramid of Menkaure , likely dating 2510 BC, was constructed of limestone and granite blocks. The Great Pyramid of Giza (c. 2580 BC ) contains a huge granite sarcophagus fashioned of "Red Aswan Granite". The mostly ruined Black Pyramid dating from

5200-784: The acidification of the soil and the accumulation of peat and bogs . After a few thousand years, the mild climate deteriorated. This left these areas uninhabited, and, consequently, relatively undisturbed to the present day. The highly acidic soil has ensured that no organic remains have survived, but the durability of the granite has meant that the remains of buildings, enclosures and monuments have survived well, as have flint tools. A number of remains were "restored" by enthusiastic Victorians and, in some cases, they have placed their own interpretation on how an area may have looked. Numerous prehistoric menhirs (more usually referred to locally as standing stones or longstones), stone circles , kistvaens , cairns and stone rows are to be found on

5304-419: The base of the chamber are the same ones that would crystallize anyway, but crustal assimilation is detectable in isotope ratios. Heat loss to the country rock means that ascent by assimilation is limited to distance similar to the height of the magma chamber. Physical weathering occurs on a large scale in the form of exfoliation joints , which are the result of granite's expanding and fracturing as pressure

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5408-418: The big difference in rheology between mafic and felsic magmas makes this process problematic in nature. Granitization is an old, and largely discounted, hypothesis that granite is formed in place through extreme metasomatism . The idea behind granitization was that fluids would supposedly bring in elements such as potassium, and remove others, such as calcium, to transform a metamorphic rock into granite. This

5512-516: The buildings themselves and its physical location. The Dartmoor landscape is scattered with the marks left by the many generations who have lived and worked there over the centuries – such as the remains of the Dartmoor tin-mining industry, and farmhouses long since abandoned. See Industrial archaeology of Dartmoor . Over half of Dartmoor National Park (57.3%) is private land; the Forest of Dartmoor being

5616-501: The centuries. Many are now used as farm buildings, while others have been abandoned and fallen into ruin. Some way into the moor stands the town of Princetown , the site of Dartmoor Prison , which was originally built by Isbell Rowe & Company, Plymouth, for prisoners of war from the Napoleonic Wars and the War of 1812 . The prison has a reputation for being escape-proof, due to both

5720-402: The chancellor of the high court, ruled: "In my judgment, on the first issue set out at [14] above, the claimants are entitled to the declaration they seek that, on its true construction, section 10(1) of the 1985 Act does not confer on the public any right to pitch tents or otherwise make camp overnight on Dartmoor Commons. Any such camping requires the consent of the landowner." A protest against

5824-407: The coldest months with mean minimum temperatures around 1 °C (34 °F). July and August are the warmest months with mean daily maxima not reaching 18 °C (64 °F). Compared with Teignmouth , which is on the coast about 22 miles (35 km) to the east, the average maximum and minimum temperatures are 3.0 °C (5.4 °F) and 2.6 °C (4.7 °F) lower respectively, and frost

5928-404: The division between S-type (produced by underplating) and I-type (produced by injection and differentiation) granites, discussed below. The composition and origin of any magma that differentiates into granite leave certain petrological evidence as to what the granite's parental rock was. The final texture and composition of a granite are generally distinctive as to its parental rock. For instance,

6032-467: The early 16th century became known as spolia . Through the process of case-hardening , granite becomes harder with age. The technology required to make tempered metal chisels was largely forgotten during the Middle Ages. As a result, Medieval stoneworkers were forced to use saws or emery to shorten ancient columns or hack them into discs. Giorgio Vasari noted in the 16th century that granite in quarries

6136-579: The first magma to enter solidifies and provides a form of insulation for later magma. These mechanisms can operate in tandem. For example, diapirs may continue to rise through the brittle upper crust through stoping , where the granite cracks the roof rocks, removing blocks of the overlying crust which then sink to the bottom of the diapir while the magma rises to take their place. This can occur as piecemeal stopping (stoping of small blocks of chamber roof), as cauldron subsidence (collapse of large blocks of chamber roof), or as roof foundering (complete collapse of

6240-684: The grotto is a highly regarded piece of Buddhist art , and along with the temple complex to which it belongs, Seokguram was added to the UNESCO World Heritage List in 1995. Rajaraja Chola I of the Chola Dynasty in South India built the world's first temple entirely of granite in the 11th century AD in Tanjore , India . The Brihadeeswarar Temple dedicated to Lord Shiva was built in 1010. The massive Gopuram (ornate, upper section of shrine)

6344-454: The height of both dams by 10 feet. Work began in December 1923, including the construction of a temporary suspension bridge near Burrator Dam to maintain traffic flow during the project. The reservoir was officially re-opened on 12 September 1928. By the 1930s the watershed on Dartmoor for the reservoir was stated to be 5,360 acres. The present-day area of the reservoir at overflow level

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6448-584: The highest parts of the moor the average annual total rainfall is over 2,000 millimetres (79 in). This compares with less than 800 millimetres (31 in) in the lower land to the east around the Exe Estuary , which is in the rain shadow of the moor. Due to the influence of the Gulf Stream snowfall is not common, though due to its high altitude it is more vulnerable to snowfall than surrounding regions. Between 1961 and 1990 Met Office data shows that there

6552-501: The integrity of the moor; however, the cost of compensating companies for these licences, which may not have been granted in today's political climate, could prove prohibitive. The military use of the moor has been another source of controversy, as when training was extended in January 2003. The national park authority received 1,700 objections before making the decision. Objectors said that Dartmoor should be an area for recreation, and that

6656-610: The landscape has been exploited for industrial purposes. In recent years, controversy has surrounded the work of industrial conglomerates Imerys and Sibelco (formerly Watts Blake Bearne), who have used parts of the moor for china clay mining. Licences were granted by the British Government but were recently renounced after sustained public pressure from bodies such as the Dartmoor Preservation Association . The British government has made promises to protect

6760-505: The late Neolithic and early Bronze Age . Indeed, Dartmoor contains the largest concentration of Bronze Age remains in the United Kingdom, which suggests that this was when a larger population moved onto the hills of Dartmoor. The large systems of Bronze Age fields, divided by reaves , cover an area of over 10,000 hectares (39 sq mi) of the lower moors. The climate at the time was warmer than today, and much of today's moorland

6864-570: The lighter color minerals. Occasionally some individual crystals ( phenocrysts ) are larger than the groundmass , in which case the texture is known as porphyritic . A granitic rock with a porphyritic texture is known as a granite porphyry . Granitoid is a general, descriptive field term for lighter-colored, coarse-grained igneous rocks. Petrographic examination is required for identification of specific types of granitoids. Granites can be predominantly white, pink, or gray in color, depending on their mineralogy . The alkali feldspar in granites

6968-474: The lower crust , rather than by decompression of mantle rock, as is the case with basaltic magmas. It has also been suggested that some granites found at convergent boundaries between tectonic plates , where oceanic crust subducts below continental crust, were formed from sediments subducted with the oceanic plate. The melted sediments would have produced magma intermediate in its silica content, which became further enriched in silica as it rose through

7072-697: The lower continental crust at high thermal gradients. This leads to significant extraction of hydrous felsic melts from granulite-facies resitites. A-type granites occur in the Koettlitz Glacier Alkaline Province in the Royal Society Range, Antarctica. The rhyolites of the Yellowstone Caldera are examples of volcanic equivalents of A-type granite. M-type granite was later proposed to cover those granites that were clearly sourced from crystallized mafic magmas, generally sourced from

7176-435: The magma is inevitable once enough magma has accumulated. However, the question of precisely how such large quantities of magma are able to shove aside country rock to make room for themselves (the room problem ) is still a matter of research. Two main mechanisms are thought to be important: Of these two mechanisms, Stokes diapirism has been favoured for many years in the absence of a reasonable alternative. The basic idea

7280-426: The magma. Other processes must produce these great volumes of felsic magma. One such process is injection of basaltic magma into the lower crust, followed by differentiation, which leaves any cumulates in the mantle. Another is heating of the lower crust by underplating basaltic magma, which produces felsic magma directly from crustal rock. The two processes produce different kinds of granites, which may be reflected in

7384-408: The magmatic parent of granitic rock. The residue of the source rock becomes a granulite . The partial melting of solid rocks requires high temperatures and the addition of water or other volatiles which lower the solidus temperature (temperature at which partial melting commences) of these rocks. It was long debated whether crustal thickening in orogens (mountain belts along convergent boundaries )

7488-622: The major part of this, owned by the Duke of Cornwall . The Ministry of Defence owns 14% (see below), 3.8% is owned by water companies (see Dartmoor reservoirs ), 3.7% by the National Trust , 1.8% by the Forestry Commission and 1.4% by Dartmoor's national park authority . About 37% of Dartmoor is common land . Dartmoor differs from some other National Parks in England and Wales , in that since

7592-405: The mantle. Although the fractional crystallisation of basaltic melts can yield small amounts of granites, which are sometimes found in island arcs, such granites must occur together with large amounts of basaltic rocks. H-type granites were suggested for hybrid granites, which were hypothesized to form by mixing between mafic and felsic from different sources, such as M-type and S-type. However,

7696-502: The moor. The most significant sites include: There are also an estimated 5,000 hut circles still surviving although many have been raided over the centuries by the builders of the traditional dry stone walls. These are the remnants of Bronze Age houses. The smallest are around 1.8 m (6 ft) in diameter, and the largest may be up to five times this size. Some have L-shaped porches to protect against wind and rain; some particularly good examples are to be found at Grimspound . It

7800-517: The new restrictions, led by local storyteller Martin Shaw, was held in January 2023. However, on 31 July the ban was overturned by the Court of Appeal. There is a history of military usage of Dartmoor dating back to the Napoleonic Wars . Today, a large British Army training camp remains at Okehampton — also the site of an airbase during the Second World War. The Ministry of Defence (MoD) uses three areas of

7904-448: The northern moor for manoeuvres and live-firing exercises, totalling 108.71 km (41.97 sq mi), or just over 11% of the National Park. Red and white posts mark the boundaries of these military areas (shown on Ordnance Survey 1:25,000 scale maps). Flagpoles on many tors in and around the ranges fly red flags when firing is taking place. At other times, members of the public are allowed access. Blank rounds may also be used, but

8008-447: The numerous small pools. Two shrimp species can be found on Dartmoor: fairy shrimp that can be found in temporary pools, and, in underground streams, very rare cave shrimp. The world's largest land slug, the Ash black , is also found. Reptiles include common lizards and adders . The farmland in the wet valleys around the edge of the moors is the most important habitat for insects, including:

8112-441: The overlying crust. Early fractional crystallisation serves to reduce a melt in magnesium and chromium, and enrich the melt in iron, sodium, potassium, aluminum, and silicon. Further fractionation reduces the content of iron, calcium, and titanium. This is reflected in the high content of alkali feldspar and quartz in granite. The presence of granitic rock in island arcs shows that fractional crystallization alone can convert

8216-702: The reign of Amenemhat III once had a polished granite pyramidion or capstone, which is now on display in the main hall of the Egyptian Museum in Cairo (see Dahshur ). Other uses in Ancient Egypt include columns , door lintels , sills , jambs , and wall and floor veneer. How the Egyptians worked the solid granite is still a matter of debate. Tool marks described by the Egyptologist Anna Serotta indicate

8320-420: The relative percentages of quartz, alkali feldspar, and plagioclase (the QAPF classification ), with true granite representing granitic rocks rich in quartz and alkali feldspar. Most granitic rocks also contain mica or amphibole minerals, though a few (known as leucogranites ) contain almost no dark minerals. Granite is nearly always massive (lacking any internal structures), hard (falling between 6 and 7 on

8424-652: The reservoir's edge while attempting to stage an escape from Dartmoor Prison to the village of Meavy . The reservoir also features in Steven Spielberg 's 2011 film, War Horse . 50°29′56.57″N 4°2′25.64″W  /  50.4990472°N 4.0404556°W  / 50.4990472; -4.0404556 Dartmoor Dartmoor is an upland area in southern Devon , South West England . The moorland and surrounding land has been protected by National Park status since 1951. Dartmoor National Park covers 954 km (368 sq mi). The granite that forms

8528-551: The risk factors in granite country and design rules relating, in particular, to preventing accumulation of radon gas in enclosed basements and dwellings. A study of granite countertops was done (initiated and paid for by the Marble Institute of America) in November 2008 by National Health and Engineering Inc. of USA. In this test, all of the 39 full-size granite slabs that were measured for the study showed radiation levels well below

8632-418: The rock's high quartz content and dearth of available bases, with the base-poor status predisposing the soil to acidification and podzolization in cool humid climates as the weather-resistant quartz yields much sand. Feldspars also weather slowly in cool climes, allowing sand to dominate the fine-earth fraction. In warm humid regions, the weathering of feldspar as described above is accelerated so as to allow

8736-414: The rocks often bear a close resemblance. Under these conditions, granitic melts can be produced in place through the partial melting of metamorphic rocks by extracting melt-mobile elements such as potassium and silicon into the melts but leaving others such as calcium and iron in granulite residues. This may be the origin of migmatites . A migmatite consists of dark, refractory rock (the melanosome ) that

8840-489: The roof of a shallow magma chamber accompanied by a caldera eruption.) There is evidence for cauldron subsidence at the Mt. Ascutney intrusion in eastern Vermont. Evidence for piecemeal stoping is found in intrusions that are rimmed with igneous breccia containing fragments of country rock. Assimilation is another mechanism of ascent, where the granite melts its way up into the crust and removes overlying material in this way. This

8944-441: The southern moor are Ryder's Hill , 515 m (1,690 ft), ( grid reference SX 660690 ), Snowdon 495 m (1,624 ft), ( grid reference SX 668684 ), and an unnamed point, 493 m (1,617 ft) at ( grid reference SX 603645 ), between Langcombe Hill and Shell Top. The best-known tor on Dartmoor is Haytor (called Hey Tor by William Crossing), 457 m (1,499 ft), ( grid reference SX 757771 ). For

9048-458: The story of a man who was making his way through Aune Mire at the head of the River Avon when he came upon a top-hat brim down on the surface of the mire. He kicked it, whereupon a voice called out: "What be you a-doin' to my 'at?" The man replied, "Be there now a chap under'n?" "Ees, I reckon," was the reply, "and a hoss under me likewise." Dartmoor is popular with local astronomers because it

9152-435: The surface than magmas of I-type granites, which are thus more common as volcanic rock (rhyolite). They are also orogenic but range from metaluminous to strongly peraluminous. Although both I- and S-type granites are orogenic, I-type granites are more common close to the convergent boundary than S-type. This is attributed to thicker crust further from the boundary, which results in more crustal melting. A-type granites show

9256-416: The surrounding lowlands. As much of the national park is covered in thick layers of peat (decaying vegetation), the rain is usually absorbed quickly and distributed slowly, so the moor is rarely dry. In areas where water accumulates, dangerous bogs or mires can result. Some of these, topped with bright green moss, are known to locals as "feather beds" or "quakers", because they can shift (or 'quake') beneath

9360-473: The surrounding sedimentary rocks during the Carboniferous period, probably about 309 million years ago. It is generally accepted that the present surface is not far below the original top of the pluton; evidence for this includes partly digested shale xenoliths , contamination of the granite and the existence of two patches of altered sedimentary rock on top of the granite. A considerable gravity anomaly

9464-522: The training disturbs the peace. Those who objected included the Open Spaces Society and the Dartmoor Preservation Association . During her lifetime, Sylvia Sayer was another outspoken critic of the damage that she perceived that the army was doing to the moor. The designated Dartmoor National Park area has a resident population of about 33,000, which swells considerably during holiday periods with incoming tourists. The largest settlements within

9568-438: The upland heaths heather ( ling ) and bell heather are common along with western gorse . In dry grassy areas tormentil , heath bedstraw and heath milkwort are all common. Cross-leaved heath and purple moor grass grow in wetter spots and in the boggy areas many different species of sphagnum and other mosses can be found, along with liverworts , Hare's-tail Cotton-grass , round-leaved sundew and bog asphodel , and in

9672-865: The uplands dates from the Carboniferous Period of geological history. The landscape consists of moorland capped with many exposed granite hilltops known as tors , providing habitats for wildlife. The highest point is High Willhays , 621 m (2,037 ft) above sea level. The entire area is rich in antiquities and archaeological artefacts . Dartmoor National Park is managed by the Dartmoor National Park Authority , whose 22 members are drawn from Devon County Council , local district councils and Government. The Dartmoor Commoners' Council exists to create and enforce regulations regarding commoners' rights. Parts of Dartmoor have been used as military firing ranges for over 200 years. The public

9776-502: The uranium washes into the sediments from the granite uplands and associated, often highly radioactive pegmatites. Cellars and basements built into soils over granite can become a trap for radon gas, which is formed by the decay of uranium. Radon gas poses significant health concerns and is the number two cause of lung cancer in the US behind smoking. Thorium occurs in all granites. Conway granite has been noted for its relatively high thorium concentration of 56±6 ppm. There

9880-599: The use of flint tools on finer work with harder stones, e.g. when producing the hieroglyphic inscriptions. Patrick Hunt has postulated that the Egyptians used emery , which has greater hardness. The Seokguram Grotto in Korea is a Buddhist shrine and part of the Bulguksa temple complex. Completed in 774 AD, it is an artificial grotto constructed entirely of granite. The main Buddha of

9984-420: The valley bottoms, many different sedges , bogbean and pale butterwort all grow. A large variety of bird species can be found on Dartmoor including ones that have declined elsewhere in the UK, such as skylark and common snipe ; some are even rare nationally, such as the ring ouzel and the cuckoo . There are internationally important populations of meadow pipit and stonechat . Woodland birds include

10088-549: The wettest patches. The valley bogs have lush growth of rushes , with sphagnum, cross-leaved heath , sundews and several other species. Some of the bogs on Dartmoor have achieved notoriety. Fox Tor Mires was supposedly the inspiration for Great Grimpen Mire in Conan Doyle's novel The Hound of the Baskervilles , although there is a waymarked footpath across it. Sabine Baring-Gould , in his Book of Dartmoor (1900) related

10192-409: Was an average of 20 days when snow fell on the moor, and over 40 days a year with hail, which is as high as anywhere else in the country. This results when cold polar maritime air that has travelled over a large expanse of warmer ocean is forced to rise over high country. When average temperatures at Princetown between 1961 and 2000 are compared, the average annual temperature in the decade 1990–2000

10296-711: Was built under the supervision of Edward Sandeman (1862-1959), the Water Engineer for Plymouth . The reservoir has two dams, the Burrator Dam, which is built across the River Meavy at Burrator Gorge at the south-western end, and the Sheepstor Dam built on a dividing ridge between the Meavy and Sheepstor Brook at the south-eastern end. The Burrator Dam was the first of the two to be built, with construction starting on 9 August 1893. It

10400-401: Was covered with trees. The prehistoric settlers began clearing the forest, and established the first farming communities. Fire was the main method of clearing land, creating pasture and swidden types of fire-fallow farmland. Areas less suited for farming tended to be burned for livestock grazing. Over the centuries these Neolithic practices greatly expanded the upland moors, and contributed to

10504-468: Was largely unaffected by the Countryside and Rights of Way Act 2000 , which established similar rights in other rural parts of the country, until 2006, when the 2000 Act opened up much of the remaining restricted land to walkers. In January 2023, in a high court judgement in a case brought by landowner Alexander Darwall , the right for members of the public to wild camp on Dartmoor was lost. Julian Flaux ,

10608-405: Was sufficient to produce granite melts by radiogenic heating , but recent work suggests that this is not a viable mechanism. In-situ granitization requires heating by the asthenospheric mantle or by underplating with mantle-derived magmas. Granite magmas have a density of 2.4 Mg/m , much less than the 2.8 Mg/m of high-grade metamorphic rock. This gives them tremendous buoyancy, so that ascent of

10712-564: Was supposed to occur across a migrating front. However, experimental work had established by the 1960s that granites were of igneous origin. The mineralogical and chemical features of granite can be explained only by crystal-liquid phase relations, showing that there must have been at least enough melting to mobilize the magma. However, at sufficiently deep crustal levels, the distinction between metamorphism and crustal melting itself becomes vague. Conditions for crystallization of liquid magma are close enough to those of high-grade metamorphism that

10816-438: Was up by 0.2 °C (0.4 °F) and the late winter temperature increased by 0.5 °C (0.9 °F). Because of Dartmoor's height and granite geology, it experiences strong winds and has acidic soils. In consequence it has been subject to very little intensive farming , and all these factors combine to form the basis of the important ecosystems found here. The landscape is one of granite with peat bogs overlying it. While

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