Aerosol —Aerosols are minute particles, such as mist, fog or smoke, suspended in the atmosphere.

Aftershock — An earthquake which follows a larger earthquake or main shock and originates at or near the focus of the larger earthquake. Generally, major earthquakes are followed by a larger number of aftershocks, decreasing in frequency with time.

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.

Amplitude — The maximum height of a wave crest or depth of a trough.

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.

Array — An ordered arrangement of seismometers or geophones, the data from which feeds into a central receiver.

Arrival — The appearance of a seismic wave on the seismic record.

Arrival time — The time at which a particular wave phase arrives at a detector.

Aseismic area — An area that is almost free of earthquakes.

Ash — Small (less than 2 mm) fragments of rock and volcanic glass ejected during volcanic eruptions.

Aseismic area — An area that is almost free of earthquakes.

Asthenosphere — The asthenosphere is the ductile part of the Earth just below the lithosphere, including the upper mantle. The asthenosphere is about 180 km thick.

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.


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.

Barrow —An ancient burial mound.

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. A plane of deposition, a surface that separates each successive layer of stratified rock.

Benthos — Animals and plants living on the bottom of a sea or lake.

Biostratigraphy — The classification of rock successions based on fossil content.

Biozones — Intervals of rock characterised by a particular fossil species or groups of species. Further subdivisions of these intervals are called Sub-biozones.

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.

Bodmin Moor — Rugged granite landscape in the hills of Cornwall in south-west England.

Body wave — A seismic wave that travels through the interior of the earth and is not related to a boundary surface.

Bronze Age — The period of British prehistory from approximately 2500–1500 BCE.


Calcite — The crystalline form of calcium carbonate, CaCO3. When pure, it is colourless and transparent, or white. It is a very common and widely distributed mineral in the Earth's crust. Small quanities of magnesium (Mg) are often included. It forms a large proportion of limestones.

Credit — The period of time between 545 and 495 million years ago.

Cambrian — The period of time between 545 and 495 million years ago.

Cambrian mountains — Mountains in north Wales made of ancient rocks such as hard slates and volcanic. See Snowdon.

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

Capillary action — The ability of water to flow through narrow spaces without the assistance of forces such as gravity.

Carbonate minerals — A group of minerals with different chemical compositions, but all containing the carbonate ion CO3. Here, we concentrate on calcite ( -CaCO3 with trigonal crystals), aragonite ( -CaCO3 with orthorhombic crystals),and 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.

Charnwood — In Charnwood Forest in Leicestershire very ancient Cambrian slates (as well as volcanic rocks) stick up above the much younger Triassic mudstones.

Cheshire Plain — Lowlands area of England, on the border with North Wales.

Cheviot Hills — In northern England, close to the Scottish Southern Uplands, the Cheviot Hills are composed of a great thickness of hard, ancient lavas and intrusions of igneous rocks, covered by a thick layer of peat.

Chitin — A complex organic compound which forms the horny outer skeleton of some creatures such as insects, crabs and lobsters.

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.

Coppicing — A traditional method of woodland management involving cutting down young tree stems almost to the ground causing new shoots to grow.

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

Correlation — The process of determining the age equivalence of two or more geographically separate rock units. Fossils are one of the most important tools for correlation.

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 here, 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.

Cross Fell — Highest point in the Pennine Hills.

Chronostratigraphy — The classification of rock successions based on relative age and time relationships.

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'.


Dartmoor — Granite landscape in the hills of Devon in south-west England.

Dendritic —Forming a pattern resembling tree branches.

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.

Dorset Downs — Part of the largest area of chalk downland in southern England.

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.


Earthquake — Shaking of the earth caused by a sudden movement of rock beneath its surface.

Earthquake swarm — A series of minor earthquakes, none of which may be identified as the main shock, occurring in a limited area and time.

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

Ecological niche — The role played by an organism in its environment, e.g. as grazer, scavenger or predator.

Elastic wave — Rock is an elastic material that when strained by normal external forces can return to its original state. When the strength of the rock is exceeded, the rock ruptures, generating elastic seismic or earthquake waves.

EMS — The currently used 12-grade European macroseismic scale (EMS-92) is the updated version of the MSK-scale intensity scale.

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.

Epicentre — That point on the Earth's surface directly above the hypocentre of an earthquake.

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.

Exmoor — An example of where hard sandstones form high hills (520 m).


Facies — The sum total of a rock's lithological and gross palaeontological characteristics that together are the product of the particular environment in which the rock formed.

Fault — A fracture in the rock along which movement takes place. A weak area in the Earth's crust where two sides of a fracture or fracture zone move relative to each other.

Faunal provincialism — Most animal species and genera do not have a worldwide distribution. Certain groups are confined to certain regions. Barriers such as sharp temperature changes or abrupt physiographic features divide the provinces, although their boundaries are rarely clear-cut.

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.

First arrival — The first recorded signal on a seismogram is the direction of the first P-wave, where upward ground motion is compressional and downward motion is dilatational.

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.

Focus — The point where earthquake rupture or fault movement originates.

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.

Forest of Bowland — An example in the southern Pennines where Carboniferous sandstones and grits form high exposed moorland areas.

Foreshock — A small earthquake that may precede a larger earthquake or main shock and that originates at or near the focus of the larger event.

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.

Frequency — The frequency of a wave (Hz) is the number of wave cycles per second.

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


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

Geological time — This is divided into eras, periods, epochs and ages. The rocks formed during these different intervals are called respectively, erathems, systems, series and stages. For example, the Turonian Stage of the Cretaceous System encompasses the rocks formed during the Turonian Age of the Cretaceous Period.

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.

Grampian Mountains — One of Scotland’s three large mountain ranges.

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.


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.

Hypocentre — The calculated location of the focus of an earthquake.


Iapetus — The precursor of the Atlantic Ocean was named after the father of Atlas.

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.

Impermeable — Rocks that do not allow water to pass through them are called 'impermeable'.

Induced seismicity — Non-natural events induced by man's activity. These include mining induced events, events caused by loading of dams or pumping of water in geothermal areas.

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

Intensity — A measure of the effects of an earthquake at a particular place on humans and (or) structures. The intensity at a point depends not only upon the strength of the earthquake (magnitude) but also upon the distance from the earthquake to the epicentre and the local geology at that point.

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.

Iron Age — The period of British prehistory from approximately 800 BCE – 100 CE.

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

Isoseismal line — A line enclosing points on the Earth's surface at which earthquake intensity is the same. It is usually elliptical in shape

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.


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.


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.


Lagerstätten — Derived from a German mining term, fossil Lagerstätten are deposits that are extremely rich in fossil material and/or contain exceptionally well-preserved specimens. A well known example is the Middle Cambrian Burgess Shale of British Columbia, Canada, which contains trilobites with their soft parts preserved.

Lake District — A mountainous area, where Scafell Pike is the highest mountain in England. Igneous rocks in the Lake District vary from granite, which forms deep underground, to ancient lavas and ash ejected from volcanoes. Metamorphosis also caused slate to form in the Lake District.

Lancashire Plain — Lowlands area of north west England.

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.

Leith Hill — One of the highest hills in the south east of England (294 m).


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 bench — A long narrow strip of level ground in a limestone landscape with steeper slopes above and below it.

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

Lithosphere — The solid rock of the Earth’s outer layers, including the crust and the upper mantle.

Lithostratigraphy — The classification of rock successions based on rock type (otherwise known as lithology).

Love wave — A major type of surface wave having a horizontal motion that is shear or transverse to the direction of propagation. It is named after A.E.H. Love, the English mathematician who discovered it.


Magnitude — A measure of the strength of an earthquake. There are several scales depending on which part of the seismogram is examined. These include Richter local magnitude (ML), Body wave magnitude (mb) and surface wave magnitude (Ms). Moment magnitude (Mw) is calculated from spectral analysis.

Maine transgressions — Advances of the sea over the land

Malvern Hills — Precambrian gneiss, a hard, highly metamorphosed rock, and schist form in these hills.

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.

Microseism — A motion in the Earth that is unrelated to an earthquake. It is caused by a variety of natural and artificial agents, for example wave action, wind, traffic and industrial noise.

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.

MSK — MSK intensity is the intensity scale used in Europe before the introduction of the EMS scale. It is a 12-grade scale ranging from not felt to complete devastation.

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


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.

North West Highlands — One of Scotland’s three large mountain ranges.


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

Oligocene — The period of time between 23 and 34 million years ago.

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.

Ordovician — The period of time between 443 and 485 million years ago.

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 wave — The first and faster of the body waves which moves by a series of compressions and dilatations, similar to a sound wave. They can travel through both solid and liquid.

Palaeobiogeography — The study of the global, regional and local distribution patterns of fossil plants and animals.

Palaeoecology — The study of the relationship between fossil plants and animals, and the environment in which they lived in the geological past.

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. Substances that allow water to pass through them are called 'permeable'.

Permian — The period of time between 252 and 298 million years ago.

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

Phase — The onset of a displacement on a seismogram indicating the arrival of the different types of seismic wave.

Phylum — A major division of the animal or plant kingdom, containing species having the same general form. Examples are Cnidaria (including corals, sea anemones and jelly fish), Echinodermata (including sea urchins, starfishes and crinoids) and Mollusca (including bivalves (clams), gastropods and cephalopods). Wikipedia entry

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.

Pinnacle karst — Karst that is characterised by remnant upstanding, blocks of limestone separated by dissolutionally enlarged joints, which may be buried by clastic sediments.

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'. The plates are continuously moving relative to each other.

Plate boundary — The place where two or more plates in the Earth's crust meet.

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.)

Prediction — Predicting the time, place and magnitude of an earthquake.

Primary porosity — Porosity a rock has when it forms. Spaces (pores) between the grains of calcite, shells, sand grains etc, and within the grains themselves (shells, corals etc have pores and holes within them).


Quantock Hills — Some sedimentary rocks such as the sandstones and grits of the Quantock Hills and Clee Hills are very hard and resist weathering and erosion.

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.


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

Rayleigh wave — A type of surface wave having a retrograde, elliptical motion at the free surface. It is named after Lord Rayleigh, the English physicist who predicted its existence.

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.

Reduced porosity — The porosity in rocks can decrease after burial. Pores are closed when the rock is squeezed and compacted underground. Porosity is also decreased by the precipitation of silica or calcite in pore spaces from percolating fluids.

Reflected wave — A wave that has turned back from a boundary or discontinuity in the earth's crust.

Refraction — The change in direction of a wave on reaching a boundary of different density and velocity.

Relative dating — Determining the age of a rock relative to another, rather than its absolute age in millions of years.

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.)

Richter scale — A popular name for the local magnitude scale (See Magnitude).

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 wave — The second arrival on a seismogram, the S wave, is slower than the P-wave. It is a shear wave and cannot travel through liquids.

Salisbury Plain — Lowlands area of southern England.

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. Holes that were made after the limestone was formed. They are usually caused by dissolution by acidic water or due to changes in the crystals (like when calcite changes to dolomite).

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. Sedimentary rocks cover more than two-thirds of the Earth's surface. They are formed from the weathering and erosion products of rock material which have been transported (usually by water or wind), redeposited and later consolidated.

Seismogram — A record of an earthquake or ground vibration. The wave trace is made up of P-waves, S-waves and surface waves, the pattern of onsets of the first two arrivals help to determine the location. The seismogram can be either a paper record or a digital record that is analysed by computer.

Seismograph — An instrument that registers the occurrence of an earthquake and the time it occurred as a written record.

Seismologist — A scientist who studies earthquakes.

Seismometer — An instrument that not only measures the time of the arrival of earthquake waves, but also allows the exact motion of the ground to be computed from the record.

Seismoscope — An instrument that registers the occurrence of an earthquake, but not the time.

Shale — A laminated mudstone formed under pressure.

Signal-to-noise ratio — The comparison between the amplitude of the seismic signal and the amplitude of noise caused by seismic unrest and (or) the seismic instruments.

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.

Southern Uplands — One of Scotland's mountainous areas, close to the border with England. North of the Cheviot Hills.

In spate — A river is described as being in spate during sudden flood conditions, such as flash floods.

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'.

Stone Age — The period of British prehistory from the earliest known inhabitation by humans to approximately 2000 BCE.

Stratigraphy — The study and classification of rock successions.

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

Subduction zone — An elongated region along which a crustal plate descends relative to another crustal block, for example, the descent of the Pacific plate beneath the Andean plate along the Andean trench.

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

Subtropical — Latitudes of the Earth adjacent to the tropics.

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

Sump — A flooded cave or passage.

Surface waves — Seismic waves with motion restricted to near the ground surface (Love and Rayleigh)

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)


Teleseism — An earthquake that is distant from the recording station.

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.

Texture —The general character or appearance of a rock as indicated by relationships between its component particles, specififcally grain size, shape, degree of crystallinity and arrangement.

A lowland area of south-east England comprised of soft Palaeogene sedimentary rocks.

The Fens — Lowlands area in eastern England.

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' but in this context it refers to some places on the moors of south-west England, where erosion has worn away the surface rocks and soil to expose granite. This forms a rock-strewn hill, high on the moors.

Travel time — The time required for a wave train to travel from its source to a point of observation.

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.

Tsunami — A huge sea wave caused by earthquakes. (Referred to by many as a tidal wave.)

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


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.


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.

Vale of Aylesbury — Lowlands area of England, composed of impermeable clay.

Vale of Belvoir and Trent Valley — Lowlands area of central England, composed of impermeable clay.

Vale of Evesham — Lowlands area of England, near the Cotswolds.

Vale of the White Horse — Lowlands area in the west of the Marlborough, Berkshire and Hampshire Downs.

Vale of York — Lowlands area of north east England, comprising soft mudstone.

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.

Volcanic earthquake — Earthquakes associated with volcanic activity.

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


Walbury Hill — One of the highest hills in the south east of England (297 m).

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.

Wavelength — The distance between two successive crests or troughs of a wave.

Weald — Lowlands area of south east England, composed of impermeable clay.

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 — The processes (chemical or physical) by which rock is broken down.

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.




Yorkshire Dales — An upland area of central northern England, the Yorkshire Dales are the central part of the Pennine chain and are made of hard and resistant fossiliferous limestones overlain by shales and hard gritstones and sandstones.


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