Copy of `BGS - Geological terms`

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BGS - Geological terms Category: Sciences > Geology Date & country: 27/12/2017, UK Words: 324

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.

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.

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.

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.

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.

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.

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

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

Gap
In limestone landscapes, 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.

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.

Focus
The point where earthquake rupture or fault movement originates.

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.

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).

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.

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.

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.

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

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.

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.

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).

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).

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.

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.

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

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.

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.

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

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

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.

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

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.

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.

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).

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

Cross Fell
Highest point in the Pennine Hills.

Cwm
see 'corrie'.

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

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

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.

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

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.

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.

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.

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.

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

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

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.

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

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

Chalk
A soft limestone formed mainly of coccolith skeletons.

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

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

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

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

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.

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).

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

Carbonaceous
A rock or sediment that is rich in carbon.

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.

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.

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

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

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

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

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

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

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

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