Glossary

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Albedo — The amount of solar radiation that is reflected back off a surface.

Alum — A chemical compound that can be processed from clays. It has been used for industrial purposes (e.g. tanning leather and dyeing) and in medicine.

Altitude — Height above sea level.

Anglian — One of the glaciations during the last Ice Age, about half a million years ago, when glaciers reached as far south as the Severn–Thames estuaries.

Anticline — Upwardly arched folds of Sedimentary rocks put under pressure by movement in the Earth. (See syncline)

Aquifer — One of many types of permeable rock. Pore spaces (tiny holes) between the grains, or fractures (cracks) allows water to flow through and accumulate in an aquifer rock.

Aquiclude — An impermeable layer of rock which water cannot flow through because there are no pore or fracture voids, or such voids are not connected together.

Aquitard — A rock with limited permeability that allows some water to pass through it, but at a very reduced rate.

Aragonite — An unstable form of calcium carbonate which changes into calcite.

Ash — In Limestone Landscapes we use this term to mean small (less than 2 mm) fragments of rock and volcanic glass ejected during volcanic eruptions.

Atmosphere — The atmosphere is a thin layer of gas and suspended particles surrounding the Earth and is composed mainly of nitrogen and oxygen but also small quantities of argon, carbon dioxide, neon, helium, methane, krypton, nitrous oxide, hydrogen, xenon and ozone (in order of decreasing amounts). The atmosphere has four layers: the troposphere up to an altitude of about 18 km, the stratosphere from 18 km to about 50 km, and the mesosphere from about 50 km to 82 km, beyond which is the thermosphere. Above 80 km the gases begin to thin out eventually leaving just oxygen in its atomic form.

Atoll — A reef that formed around an island. The island sank, but the continued growth of the coral resulted in a rounded reef.

s

B

Barrier reef — A coral reef that started growing close to the shore (fringing reef), but due to earth movements is now growing some distance away from it.

Basin mires — Developed in a waterlogged basin which may be completely enclosed or only a very restricted through-flow of water.

Bed — Layer of sedimentary rock. Beds are built up one on top of the next, separated from each other by bedding planes. Each bed represents a single phase of more or less continuous sedimentation, before a change in conditions or an interruption of sedimentation, forms the bedding plane.

Bedding plane — A surface occurring in sedimentary rocks that represent an event that interrupted sedimentation for a time.

Blanket mires — Formed on extensive flat or gently sloping ground usually in 'upland' ground.

Blind valley — Formed by erosion at a swallow hole, resulting in an uphill facing cliff and a dry valley further down hill.

C

Calcite — Calcium carbonate (CaCO3 ). It forms a large proportion of limestones.

Cambrian — The period of time between 545 and 495 million years ago. Calcium carbonate (CaCO3 ). It forms a large proportion of limestones.

Carbonate Minerals — A group of minerals with different chemical compositions, but all containing the carbonate ion CO3. In Limestone Landscapes, we concentrate on Calcite -CaCO3 with trigonal crystals, aragonite -CaCO3 with orthorhombic crystals, Dolomite CaMg(CO3).

Carboniferous — A period of time between 290 and 354 million years ago.

Carbonaceous — A rock or sediment that is rich in carbon.

Carbon cycle — The natural cycling of carbon atoms between rocks, vegetation, oceans and the atmosphere.

Carbon sink — A part of the carbon cycling where carbon accumulates such as in calcium carbonate rocks.

Catchment area — The region from which a river receives its water supply. The margin of the area is usually the hill tops that surround it, called the watershed or divide (beyond this water flows away into other river systems).

Cement — The material, usually a very fine-grained mineral growth, which forms after a rock is deposited and bonds the grains of sediment together.

Chalk — A soft limestone formed mainly of coccolith skeletons.

Clay — A sedimentary rock with grains smaller than 0.002 millimeters in diameter and plastic when wet. Its main mineral is hydrated silicates of aluminium. It is often used to manufacture bricks and pottery.

Climate — Average atmospheric conditions of an area. This is controlled by the latitude of the area, which determines how much solar radiation it receives, the distribution of land masses and oceans, the altitude and topography of the area, and the influence of ocean currents. See weather.

Clints — A rectangular block of limestone in a limestone pavement, separated from the neighbouring blocks by fissures (clints).

Coal — A fossil fuel comprising rocks with a large proportion of fossil plant remains that have been altered to carbon.

Coccoliths — Calcareous skeletons of microscopic, single celled, photosynthesising algae called coccolithophores.

Cockpits — A karst feature in hot humid countries comprising small, rounded or conical hills (up to 120 m high), with star-shaped depressions between. They occur in groups of up to 30 per square kilometre.

Combe — A hollow or short valley in the side of limestone uplands or chalk down lands in southern England.

Coral reef — A structure rising from the sea floor composed of the calcareous skeleton of corals.

Corrie — A large, semi-circular hollow in the side of a mountain that was eroded by the action of snow and ice. Corries are found in areas where glaciers once formed. In Wales this type of hollow is called a 'cwm' but the French name 'cirque' is used by some people.

Crag — In the sense used in limestone landscapes, a cliff of limestone on the side of a hill or steep valley.

Cretaceous — The period of time about 65 and 142 million years ago.

Crust — The outermost solid layer of the Earth up to about 70 km thick. There are two types: continental crust (which is older and thicker) and oceanic crust (which is younger and much thinner).

Cwm — see 'corrie'.

D

Devonian — A period of time between 354 and 417 million years ago.

Diagenesis — The process that changes sediment into rock. This happens by the water being squeezed out, mineral grains being organised or chemically changed and the whole being cemented by minerals precipitated from peculating mineralised water.

Diatoms — Single celled algae that have interlocking cell walls made of silica.

Dip slope — see escarpment.

Dolerite — A dark coloured igneous rock, intruded into the earth's crust, with medium sized crystals of feldspar, pyroxene and other, less common, minerals.

Doline — A depression or hole in the ground formed by the solution of limestone by chemical weathering.

Dolomite — A mineral of magnesium carbonate. See dolostone.

Dolostone — A rock that comprises over 90% of the mineral dolomite. The rock used to be called dolomite, but as it was possible to confuse dolomite (the rock) with dolomite (the mineral), it was decided that the rock should have a different name.

Dry valley — A valley that was formed by rivers when the water table was high or when the ground was frozen, but now abandoned by the river.

E

Eccentricity — The Earth's orbit around the sun changes from being almost circular to elliptical in shape every 100 000 years.

Enhanced Greenhouse effect — 'Greenhouse gases' are actually crucial to keeping our planet at a habitable temperature, without them the Earth would be about minus 17 degrees! Anthropogenic or human release of carbon dioxide is what is contributing to an additional or enhanced greenhouse effect.

Erosion — Erosion is the wearing away of the Earth's surface by the sea, rivers, glaciers and wind. The important point to remember is that erosion causes the breakdown of the rock and then the transportation of the rock fragments. Weathering processes do not involve transportation.

Erratic — A block of rock that has been eroded by a glacier, transported by the ice to a distant locality and then dumped as the glacier retreated. Erratics may have been carried many kilometres. In this way a boulder of one age may be found resting on rocks of a different type and a different age. An older block might be found on top of a younger rock.

Escarpment — A long hill, or ridge, composed of gently dipping beds of rock. One side of the hill is gently sloping ('dip-slope') and the other side of the hill is very steep (scarp-slope).

Estavelles — A sink hole where water disappears below ground during part of the year, but from which water issues during storms and winter floods (when the underground drainage system exceeds its capacity).

Eustasy — A global change in sea level. Compare with Isostasy.

Evolution — The change in the characteristics of living organisms over successive generations, it occurs through the mechanism of natural and sexual selection.

F

Fault — A fracture in the rock along which movement takes place.

Fengcong — A Chinese form of tower karst. Hills or towers are joined at their base and have deep depressions between.

Fenglin — Similar to fengcong, but the towers are not joined at the base, but have valleys around.

Flint — A rock composed of the cryptocrystalline form of silica. In Britain it is often associated with Chalk.

Floodplain mires — Developed on waterlogged, periodically inundated river and stream floodplains and on coastal plains behind beach barriers and salt marsh. Often very extensive and include one or more buried peat sequences.

Foraminifera — Single-celled organisms (protists) with a hard shell. Minute single celled 'armoured amoeba' (protoctista) that secrete a calcareous shell and live in the sea.

Fossil — Originally meaning anything dug from the ground, the term fossil is now restricted to naturally preserved evidence of an ancient organism. These include preserved parts of the original organism (such as bones, skin, hair, shell, teeth, leaves, bark, pollen), an imprint of a body part (such as the hollow left by a dissolved shell, or a footprint), or some other trace (such as mineralised dung, worm-casts or burrows).

Fossil fuels — A stored energy source, originally of organic (living) origin, that can be used as a fuel; includes coal, oil, natural gas, and peat.

Fringing reef — A coral structure that is built up along the coast of an island or land mass.

G

Gap — In limestone landscapes, this is a break in a ridge of hills.

Glacial — Characterised or produced by the presence or action of ice. A period of glaciation. See Interglacial.

Glacier — A mass of ice and snow which can deform and flow under its own weight. A 'river' of ice that flows down valleys towards the sea. In Britain glaciers formed during the last Ice Ages and caused erosion in upland areas (forming the typical U-shaped profile of valleys). The eroded rock debris was dumped when the ice melted to form moraine.

Gneiss — (pronounced 'nice'). A metamorphic rock that has been subjected to such great pressures that new crystals have replaced the original ones. The original rock approached melting point, and, as a result, changed to this granite-like rock with banding of different crystals.

Gorge — A steep sided valley cut by rivers often during periglacial conditions. Several in Britain (e.g. Cheddar Gorge) were thought to have formed when caverns collapsed, but this is now known not to be the case.

Granite — A hard igneous rock that formed deep (several kilometres) underground. It formed from magma that cooled slowly so that the crystals grew to a large size (these are mainly quartz, feldspar and mica). The granites we see at the surface today were exposed when overlying rocks were worn away by erosion.

Greenhouse effect — The natural 'trapping-in' of heat by greenhouse gases present in the atmosphere.

Greenhouse gas — A greenhouse gas is so-called because it absorbs infrared radiation emitted by the Earth's surface (the original energy source for this radiation is solar radiation), the absorbed radiation is trapped as heat in our atmosphere. Greenhouse gases in our atmosphere are: carbon dioxide, water vapour, methane, nitrous oxide, ozone and CFCs.

Grit — A sediment comprsing coarse sand grains.

Gritstone — A coarse-grained sandstone.

Groundwater — Water found underground within porous soils and rocks.

Gryke — Fissures in a limestone pavement. These fissures were formed beneath a soil cover by chemical weathering and are sometimes over a metre in depth. Grikes may form a microenvironment where unusual plant may grow, including alpine plants that have managed to live in this protected environment since the last Ice Ages.

H

Holocene — The time period from 10 000 years ago to the present day.

Hum — A conical residual hill (formed by solution) that penetrates through the sediment that covers the otherwise flat floor of poljes.

Hydrological cycle — The movement of water through the environment by the processes of evapotransporation, condensation, wind transportation, precipitation, runoff, infiltration and interception.

Hydrostatic pressure — The weight of the water higher in the cave system, exerts a pressure on the water lower down, forcing it to flow through passages and up joints towards regions of low hydrostatic pressure, such as resurgences.

I

Ice age — A long period of glaciation. An informal term for a time when global temperatures were greatly reduced and glaciers, ice fields, pack ice, etc advanced. There have been several 'ice ages' during the last 600 million years or so. The last one to affect Britain occurred during the last million years (ending about 10 000 years ago). This was a time of contrasts between phases of glaciation interspersed by warmer phases (sometimes warmer than today).

Ice sheet — A glacier of more than 50 000 km2 with a flattened dome that buries the landscape.

Igneous rock — A rock that originated when a molten magma or lava cooled and solidified.

Infilitration — The downward flow of surface water into the soil.

Interglacial — A phase of relatively warm temperatures between glacials. See glacial.

Interpolated / Interpolation — The process by which software invents new data to fill gaps in an image or grid.

Ironstone — A mudstone or sandstone with a high iron content.

Isostasy — The theoretical equilibrium that tends to exist in the Earth's crust; this can alter sea level on a local scale. For example, glacial ice can push down the crust so that when it melts the crust will uplift thus causing sea level in the area to decline. Compare with Eustasy.

Isotopes — Atoms of an element that have the same number of electrons and protons but different numbers of neutrons.

J

Joints — Fissures in rocks, often at right angles to each other and the bedding planes, formed as a result of deformation.

Jurassic — The period of time between 142 and 205 million years ago.

K

Karren — Small hollows on the surface of limestones (e.g. limestone pavements) caused by solution during chemical weathering.

Karst — The term given to a distinctive landscape created by the solution and erosion of a soluble rock such as limestone. Water is an essential ingredient in the formation of the characteristic topographical features (dolines, caves, dry valleys, etc).

Kufeng — Towers similar to fenglin, but isolated from the other towers by a flat plain.

L

Latitude — Circles drawn around the Earth parallel to the equator; their diameters diminish as they approach the poles. These parallels have an angle provided from the angle from the equator i.e. 0 degrees at the equator and 90 degrees at the poles.  

Lava — Molten magma that extrudes onto the Earth's surface as a result of a volcanic eruption. The lava solidifies quickly to form a hard, very fine grained rock. Gases within the magma may form large voids, sometimes filled with minerals and crystals.

Lead_ore — A rock sufficiently rich in lead that it is mined.

Limestone — A hard sedimentary rock that is composed of over 50% carbonate minerals. A true limestone is over 90% calcite, but there are often other carbonates (including dolomite) and impurities in the form of sand grains, clay minerals, etc. Limestone is laid down in layers or 'beds' separated by 'bedding planes' and divided up into blocks by a series of joints (fissures created during the rock formation process) at approximately, right angles to each other.

Limestone pavement — A flat expanse of exposed limestone formed by a combination of erosion and chemical weathering.

M

Maine transgressions — Advances of the sea over the land

Mantle — Inside the earth, the layer below the earth's crust but above the core                    

Marine regressions — Retreats of the sea over the land

Massive limestones — Limestones that are made of thick layers (called beds) of rock. In Britain, the Carboniferous Limestone is the best examples. Other limestones such as the Cretaceous chalk and Jurassic limestones of Central England are made of thin beds and can not described as massive.

Mesozoic — An era in which the Triassic, Jurassic and Cretaceous periods are grouped (65 to 248 million years ago).

Metamorphic rock — A 'changed rock', altered by heat and or pressure so that mineral grains are preferentially orientated or new types of crystals begin to grow.

Metamorphism — When a pre-existing rock is chemically or physically altered by heat, pressure or chemically active fluids.

Mogote — Like a hum, but in tropical areas. It is a residual hill sticking up through the sediment as a result of karstic processes.

Moraine — The material eroded by a glacier and carried along by the ice, before being dumped when the glaciers retreat. Till is one type of moraine. Erratics originated as moraine.

Mudstone — Muds and silts that have been compressed to form a hard, fine-grained rock.

N

Negative feedback — A process that is triggered by an initial change in an environmental variable so that the original 'normal' condition is restored. See positive feedback.

O

Obliquity — Earth rotates around an axis; the angle of this axis changes from 22.1 to 24.5 degrees.

Ooidal limestone — A limestone that is formed of abundant ooids (sometimes called ooliths), small spheres of calcium carbonate that look like fish eggs. This is sometimes called 'oolitic limestone'

Ooids — Spherical grains that formed when aragonite is precipitated in concentric layers in gently agitated water. They usually have a sand grain or shell fragment in the core.

Ombrogenous mires — Have a high-water table maintained by precipitation.

Open water transition mires — Developed from encroachment of vegetation around bodies of open water.

Orogeny — The process of mountain formation, especially by a folding and faulting of the earth's Crust.

Oxidised —  A chemical reaction with oxygen or where electrons are lost. See reduced.

P

Palaeogene — The period of time between 24 and 65 million years ago.

Peat — A thickness of partially decayed vegetation, formed in wet anaerobic ground.

Permafrost — Permanently frozen ground in polar regions. It forms in regions close to, but not under, ice caps, ice fields and glaciers. The frozen conditions may be several tens of metres thick, but the top layer may thaw in the summer months before freezing again in the winter. During the last Ice Age, much of southern Britain was affected by permafrost.

Permeability — The ability of a fluid, like water or oil, to pass from one pore space to another.

Permitted reserves — Mineral deposits with the benefit of planning permission for extraction.

Photosynthesis — The process by which plants convert light energy to chemical energy. Carbon dioxide and water are changed into carbohydrates and oxygen in the presence of light and chlorophyll.

Phreatic — (adjective) describes a cave, passage or cave system that formed below the water table and was consequently permanently flooded. The phreatic zone (or phreas) is the zone permanently saturated by water below the water table.

Planning permission — Formal approval sought from a council, often granted with conditions, allowing a proposed development to proceed. Permission may be sought in principle through outline plans, or be sought in detail through full plans.

Plate — The Earth's crust is made out of a number of huge rafts of rock. Some have continents on them and others are covered by oceans. These huge slabs are called 'plates'.

Plateau — Flat-topped area of high ground.

Plate tectonics — The Earth's surface (crust) is divided into huge fragments called tectonic plates which carry the continents on top of them. They move very slowly over the globe, past each other, away from each other or colliding and taking the continents with them.

Pleistocene — The main epoch of the last Ice Ages, between 10 000 years and 1.8 million ago, during which continental glaciers periodically expanded to cover sub-polar regions in both hemispheres.

Pleistocene (Quaternary) glacial episodes — The period from 2 500 000 to 10 000 years ago, during which continental glaciers periodically expanded to cover sub-polar regions in both hemispheres.

Poljes — A very large, closed, flat-bottomed depression formed by karstic processes in temperate regions. Rivers may flow across them, and disappear down a sink hole called a ponor.

Ponor — A cave or a sink hole in the low point of a polje, down which a river or stream disappears.

Pore space — Spaces or voids between grains in the rocks in which air, water, other fluids or fine-grained mineral cements can be present.

Porosity — The proportion of a rock that comprises spaces, voids and cracks (known as pores) between the grains.

Positive feedback — A process that is triggered by an initial change in an environmental variable which causes that variable to deviate further from the original condition. See negative feedback.

Precambrian — The period of time before animals with skeletons and shells had evolved. It stretched from the formation of the Earth about 4600 million years ago to 545 million years ago.

Precession — The slow circular movement, or 'wobble', of the Earth's axis of rotation around another axis.

Precipitation — When salts or minerals, such as calcite, come out of solution and are deposited on a rock surface. (The word also has another sense, meaning rain or snow, but that is not used here.)

Primary porosity — Porosity a rock has when it forms.

Q

Quartzite — The rock that forms when sandstone is metamorphosed by heat and/or pressure when buried within the Earth's crust. Also sometimes used to describe very pure forms of unmetamorphosed sandstone.

R

Raised mires — Developed from another mire type, commonly from a basin or floodplain mire to be above the general groundwater influence.

Recharge — The natural process in which aquifers are replenished by rainwater reaching the water table.

Reduced — The loss of oxygen or gain of electrons in a chemical reaction. See oxidised.

Relief — The difference in height in different parts of the world's surface.

Residence time — The length of time an element spends in a storage place (sink).

Respiration — The breakdown or organic compounds which releases energy and produces carbon dioxide and water.

Resurgence — Where a river or stream that has fallen into a cave system, returns to the surface. (Exurgence is where only percolated water returns to the surface and the term 'spring' refers to the point where any underground water returns to the surface.)

Ridge and corridor — A karstic feature in hot, arid regions, comprising a series of low ridges (up to 6 m high) separated by flat-floored basins (up to 1 km wide and several kilometres long).

Rock head boreholes – Boreholes that record rock head (RH) prove the base of the superficial deposits. These boreholes go all the way through the superficial and into the bedrock geology below.

S

Sandstone — As the name implies, sandstone is formed of sand that has been turned to stone. The grains of this sedimentary are mainly quartz or feldspar and cemented together with minerals such as calcite, silica or iron to form a rock. The grains are as small as 0.06 mm (1/16th mm) and as large as 2.0 mm in size. Colour varies from white to orange, red, brown, green and grey depending on the minerals present. The original sand that makes up the sandstone may have been deposited in deserts, lakes, rivers, deltas or shallow seas. Different names are given to sandstones depending on variables such as the shape, size and composition of the grains.

Scar — A vertical cliff of limestone that form along the sides of valleys.

Scarp slope — see escarpment.

Scree — A pile of rubble along the base of a steep valley, crag or cliff composed of small pieces of rock and gravel that have fallen down from above due to weathering. The rock usually becomes detached as a result of freezing and thawing. (The word 'talus' is sometimes used instead of scree, but strictly speaking, talus is made of large pieces of rock).

Schwingmoor — Floating rafts of peat.

Sea  level — Sea level or mean sea level as it is sometimes known, is the average height of the ocean's surface between high and low tide. Changes in tides and wave conditions over time are averaged out to determine a 'still water level' that can be used to identify a real change in sea level or a change in the height of the land that a tidal gauge is measuring. In the UK, height above sea level is defined as 'Ordnance Datum' and this is the mean sea level at Newlyn Bay in Cornwall.

Secondary porosity — Porosity that results from processes that occur after the rock has formed , such as fracturing or the more soluble grains dissolving.

Sedimentary rock — Rocks that originated from the broken up or dissolved and reprecipitated particles of other rocks. Examples include clay, mudstone, siltstone, shale, sandstone, limestone and conglomerate.

Shale — A laminated mudstone formed under pressure.

Sill — Intrusive igneous rocks parallel to bedding. An example is the Whin Sill in Northumberland.

Silurian — The period of time between 417 and 443 million years ago.

Sink hole — A basin in limestone areas down which water disappears. Other names include swallow hole, swallet or doline.

Slate — A metamorphic rock that was originally deposited as clay, but due to intense pressure, the platy clay minerals were orientated at right angles to the direction of pressure, resulting in the characteristic 'slaty cleavage'. The rock appears to be made of many leaves, like the pages in a book. The rock can be split into thin sheets and used to roof buildings.

Soligenous mires — Have a high-water table maintained by lateral water movement.

Solution — A salt or mineral that has dissolved and held in water.

Spatial — The location of an object, its size, shape and relationship to other objects.

Speleothems — Precipitated calcite. It takes on many different shapes depending on local conditions and include straws, stalactites, stalagmites, columns, curtains, flowstone, etc. They are formed by the precipitation of calcium carbonate (calcite) from mineral-rich water that percolates through the limestone into a cave.

Spring mires — Often small, developed downslope of springs and seepage lines.

Spring — A point in the hillside where water seeps or bubbles from the limestone. It differs from a resurgence, where a stream or river emerges and it differs from exurgence, where only percolating rain water emerges.

Stalactites — Deposits of calcite that form elongate cones at the sites of precipitation on the ceiling of a limestone cave. The word comes from the Greek stalaktos meaning dripping. Some people find it difficult to remember the difference between a stalactite and a stalagmite. It might help to remember that a 'stalactite' forms on the ceiling and that '-tites' hold tight to the cave roof.

Stalagmites — Deposits of precipitated calcite that form elongate, vertical projections on the cave floor. The word derives from the Greek stalagmos meaning 'dripped off'. Some people find it difficult to remember the difference between a stalactite and a stalagmite. It might help to remember that a 'stalagmite' forms on the ground and that ' -mites' might reach up to the '-tites'.

Structure — There are several definitions, but in Limestone Landscapes this refers to the folds and faults in rocks that have been caused by Earth movements.

Subpolar — Latitudes of the Earth adjacent to the Arctic and Antarctic circle.

Subtropical — Latitudes of the Earth adjacent to the tropics.

Suffusion — The process of washing soil down an underlying fissure (in massive limestone areas this is usually a joint).

Sump — A flooded cave or passage.

Swallow hole — A type of doline into which a river or stream descends.

Syncline — A downward fold of sedimentary rock put under pressure by Earth movements. (See anticline)

T

Temperate forests — Forests in the temperate (mild, not extreme) climate zones.

Terminal depth borehole — Boreholes that record terminal depth (TD) are boreholes that end before going through the base of the superficial deposits. These boreholes can't prove the base of the superficial deposits, but can provide a minimum value for thickness.

Thurrock ASCII grids — This folder contains the export of the Thurrock Sample Model data as a non-proprietary ascii (ESRI) grid with a cell size of 20 metres. Each geological unit is represented by its top, base and thickness.

Thurrock ESRI shells — This folder contains the export of the Thurrock Sample Model data as a proprietary (ESRI) multipatch shapefile. Each geological unit is represented by a shell or skin created from triangles.

Thurrock Gocad surfaces — This folder contains the export of the Thurrock Sample Model data to Gocad as tsurf files.

Till — (called 'boulder clay' in the past) Formed as moraine that was dumped from a glacier when the ice retreated. It comprises muds, silts and sands mixed with pebbles and boulders.

Topogenous mires — Have a high-water table maintained by the generally low lying ground.

Topography — Description on maps, etc, of natural features (hills, rivers, etc) and features made by humans (e.g. buildings, roads and railways).

Tor — There are several definitions of 'tor' and the meaning used in "Limestone Landscapes" is given here. In some places on the moors of south-west England, erosion has worn away the surface rocks and soil to expose granite . This forms a rock-strewn hill, high on the moors.

Travertine — A coarsely crystalline limestone that forms by chemical precipitation. It is often translucent and banded.

Triassic — The period of time between 205.7 and 248.2 million years ago.

Tufa — A fine grained, porous limestone formed by chemical precipitation, often around springs.

U

Unconsolidated — A sediment is unconsolidated if the particles are not attached together at all. As a sediment becomes more rock like it becomes more consolidated.

U-shaped valley — The term given to a valley when it has been eroded by glaciers. Its cross-section is U-shaped.

Uvalas — Enclosed depressions with uneven floors that are formed by solution of the limestone. They may be where several dolines are joined together or they form when small dolines form within a larger one.

V

Vadose — (adjective) Describing a passage or cave above the water table that is free draining or dry (although it may have a river flowing through it, the passage is not entirely flooded — there is air above the surface of the water). The vadose zone is the zone of rock above the water table.

Valley mires — Elongate in form, developed on the lower slopes and floors of small valleys and channels with a through-flow of water along the main drainage axis. The water table is maintained, at least partly, by springs and seepage along the valley sides.

Vruljas — Underwater springs formed when high hydrostatic pressure forces rivers to flow out of the ground below the water table.

W

Water table — The level below which the pore spaces of the soil or rocks are completely saturated with water. The horizon under the ground, below which all the pores, fissures and joints are filled with ground water. Above this horizon, the pores, fissures and caves are free draining (vadose zone) and below it they are permanently saturated (phreatic zone). Where the water table comes to the surface of the ground, spring lines, resurgence and exurgence occur.

Weather — The physical conditions of the atmosphere (mainly the troposphere) with regard to wind, temperature, cloud cover, fog and precipitation (rain, hail, snow) at a specific time and place. It is highly variable and can be unpredictable. Compare with climate.

Weathering (chemical) — The process by which rock is broken down by changes in the mineral composition, mainly as a result of acidic rainfall.

Weathering (mechanical/physical) — Rock is broken up into small pieces by wind, water or ice.

Web Coverage Service (WCS) — Is a standard interface for the querying and manipulation of geospatial coverage data, and for the serving of that data as georeferenced objects, over the web. Coverages can be a set of data points; a regular grid of points (or pixels); a set of segmented curves (eg. road paths); a set of Thiessen polygons; or a TIN triangulated irregular network (eg. terrain models). These data locations can also carry range information data - eg. a terrain model would include height information.

Web Feature Service (WFS) — Is a standard interface for the querying and manipulation of geospatial vector data and for the serving of that data as georeferenced features, using Geography Markup Language (GML), over the web.

Web Map Service (WMS) — Web Map Service (WMS) - Is a standard interface for the querying of geospatial data and for the serving of that data as georeferenced images (such as png, gif or jpeg) over the web.

X

 

Y

 

Z

Zinc ore — A rock sufficiently rich in zinc to make it worth while mining.