Misplaced Pages

#420579

34-661: The Three Towers Hike is a Scouting-organised, downland hiking competition held annually in early spring, covering footpaths in West Berkshire and South Oxfordshire . It is organised by a team of scout leaders from Reading Central, Loddon, Taceham Hundred and Pang Valley Scout Districts, all of which are within the Scout County of Royal Berkshire of the Scout Association . It is a competitive event, without an overnight camp (although teams must be equipped to bivouac if

68-507: 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 . Upper Cretaceous The Late Cretaceous (100.5–66 Ma ) is the younger of two epochs into which the Cretaceous Period

102-440: 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

136-567: 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

170-631: A northward course towards Asia. In the Southern Hemisphere, Australia and Antarctica seem to have remained connected and began to drift away from Africa and South America. Europe was an island chain. Populating some of these islands were endemic dwarf dinosaur species. In the Late Cretaceous, the hadrosaurs , ankylosaurs , and ceratopsians experienced success in Asiamerica (Western North America and eastern Asia). Tyrannosaurs dominated

204-426: 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

238-445: A slightly different route. The competitions are identified below. The hike does not prescribe a specific route for hikers to use. It publishes a series of checkpoints from which a navigation exercise will deduce the best route to take. In most cases there is usually one obvious path, however, there are some sections where a choice can be made by the navigator. Records do not include times before 2003. The Three Towers Hike has adopted

272-536: A very different dinosaurian fauna, with most predators being abelisaurids and carcharodontosaurids ; and titanosaurs being among the dominant herbivores. Spinosaurids were also present during this time. Birds became increasingly common, diversifying in a variety of enantiornithe and ornithurine forms. Early Neornithes such as Vegavis co-existed with forms as bizarre as Yungavolucris and Avisaurus . Though mostly small, marine Hesperornithes became relatively large and flightless, adapted to life in

306-579: Is divided in the geologic time scale . Rock strata from this epoch form the Upper Cretaceous Series . The Cretaceous is named after creta , the Latin word for the white limestone known as chalk . The chalk of northern France and the white cliffs of south-eastern England date from the Cretaceous Period. During the Late Cretaceous, the climate was warmer than present, although throughout

340-712: 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

374-474: Is it particularly evident that a true systematic decline was ever in place, especially with the discovery of smaller pterosaur species. Several old mammal groups began to disappear, with the last eutriconodonts occurring in the Campanian of North America . In the northern hemisphere, cimolodont , multituberculates , metatherians and eutherians were the dominant mammals, with the former two groups being

SECTION 10

#1732868983421

408-487: 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

442-500: 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

476-606: The 1970s, when only the Senior event was available. Originally, based around the North and West of Reading, the hike gets its name from the three large water towers that were passed. In the 1980s, the route was significantly altered to include more rural paths in West Berkshire and South Oxfordshire . Since its beginning, the Hike has run every year with few exceptions, the most notable being in 2001 due to Foot and Mouth concerns and 2020-3 due to

510-571: The Covid Pandemic. Officially not against the hike rules at the time, one team on the 2002 Junior Event swam across the River Thames during the race after finding themselves several miles up stream of the nearest bridge. The team then went on to complete the event but were later disqualified, and a new hike rule was added to prohibit this in the future. The Hike currently comprises four different competitions, each of different lengths and following

544-813: The Cretaceous Period derived from the German name Kreidezeit , and T is the abbreviation for the Tertiary Period (a historical term for the period of time now covered by the Paleogene and Neogene periods). The event marks the end of the Mesozoic Era and the beginning of the Cenozoic Era. "Tertiary" being no longer recognized as a formal time or rock unit by the International Commission on Stratigraphy ,

578-637: 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

612-847: The K-T event is now called the Cretaceous—Paleogene (or K-Pg) extinction event by many researchers. Non- avian dinosaur fossils are found only below the Cretaceous–Paleogene boundary and became extinct immediately before or during the event. A very small number of dinosaur fossils have been found above the Cretaceous–Paleogene boundary, but they have been explained as reworked fossils , that is, fossils that have been eroded from their original locations then preserved in later sedimentary layers. Mosasaurs , plesiosaurs , pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through

646-553: The Scout Association's branding style including the use of the SerifBlack font family in Scout Purple and Green. Its self-developed i.Hike brand has raised the event's visibility and is now recognisable as part of the hike's identification. The Three Towers Hike's tagline is "Outdoors, Challenge, Adventure". This was created to convey the core values of the competition. Downland The largest area of downland in southern England

680-519: The boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater , in combination with increased volcanic activity , such as that recorded in

714-468: 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

SECTION 20

#1732868983421

748-522: The conditions are severe enough to warrant it). It was first held as a senior event (Walkers over the age of 18) but now includes three other age groups. The hike usually takes place on the second or third Saturday in April, but this may vary depending on the timing of Easter. The event accepts registration from 1 November the previous year. Following Covid the first return of the event is scheduled for 14 October 2023. The first Three Towers Hike took place during

782-491: 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

816-742: 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

850-591: 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

884-423: 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

918-646: The large predator niche in North America. They were also present in Asia, although were usually smaller and more primitive than the North American varieties. Pachycephalosaurs were also present in both North America and Asia. Dromaeosaurids shared the same geographical distribution, and are well documented in both Mongolia and Western North America. Additionally therizinosaurs (known previously as segnosaurs) appear to have been in North America and Asia. Gondwana held

952-636: The most common mammals in North America. In the southern hemisphere there was instead a more complex fauna of dryolestoids , gondwanatheres and other multituberculates and basal eutherians ; monotremes were presumably present, as was the last of the haramiyidans , Avashishta . Mammals, though generally small, ranged into a variety of ecological niches, from carnivores ( Deltatheroida ), to mollusc-eater ( Stagodontidae ), to herbivores (multituberculates, Schowalteria , Zhelestidae and Mesungulatidae ) to highly atypical cursorial forms ( Zalambdalestidae , Brandoniidae ). True placentals evolved only at

986-531: The numerous teleost fishes, which in turn evolved into new advanced and modern forms ( Neoteleostei ). Ichthyosaurs and pliosaurs , on the other hand, became extinct during the Cenomanian-Turonian anoxic event . Near the end of the Cretaceous Period, flowering plants diversified. In temperate regions, familiar plants like magnolias , sassafras , roses , redwoods , and willows could be found in abundance. The Cretaceous–Paleogene extinction event

1020-407: The open sea. Though primarily represented by azhdarchids , other forms like pteranodontids , tapejarids ( Caiuajara and Bakonydraco ), nyctosaurids and uncertain forms ( Piksi , Navajodactylus ) are also present. Historically, it has been assumed that pterosaurs were in decline due to competition with birds, but it appears that neither group overlapped significantly ecologically, nor

1054-527: The period a cooling trend is evident. The tropics became restricted to equatorial regions and northern latitudes experienced markedly more seasonal climatic conditions. Due to plate tectonics , the Americas were gradually moving westward, causing the Atlantic Ocean to expand. The Western Interior Seaway divided North America into eastern and western halves; Appalachia and Laramidia . India maintained

Three Towers Hike - Misplaced Pages Continue

1088-433: The very end of the epoch; the same can be said for true marsupials . Instead, nearly all known eutherian and metatherian fossils belong to other groups. In the seas, mosasaurs suddenly appeared and underwent a spectacular evolutionary radiation. Modern sharks also appeared and penguin-like polycotylid plesiosaurs (3 meters long) and huge long-necked elasmosaurs (13 meters long) also diversified. These predators fed on

1122-537: Was a large-scale mass extinction of animal and plant species in a geologically short period of time, approximately 66  million years ago (Ma). It is widely known as the K–T extinction event and is associated with a geological signature, usually a thin band dated to that time and found in various parts of the world, known as the Cretaceous–Paleogene boundary (K–T boundary). K is the traditional abbreviation for

1156-603: 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 ,

#420579