Agglomerate: A rock type formed from a combination of fragments of debris produced from explosive volcanic activity.

Alluvial Fan: A fan shaped deposit that forms when a fast flowing stream flattens and slows down, typically spreading out into a fan shape.

Ammonite: A now extinct marine animal that is related to the modern nautilus.

Amphibians: A cold blooded vertebrate.  The larvae live in water and breathe using gills, the adults live on both land and water and breathe using lungs.

Amygdaloidal Basalt: Bubble, or vesicles, in lava (in this case basaltic lava) that have been filled with minerals.

Antrim Lava Group: A sequence of successive lava flows that occurred 62 – 60 million years ago during the Palaeogene Period.

Antrim Plateau: A large flat area that is elevated in comparison to the surrounding terrain.

AONB: Area of Outstanding Natural Beauty.

Arches: A geological formation which will eventually collapse to form a stack or a stump. It forms as a result of erosion, usually at the coast from the waves.

ASSI: Area of Special Scientific Interest.


Basal Conglomerate: A conglomerate that is present at the base of a sequence which is laid down during marine transgressions above an unconformity.  They represent the position of the shoreline at a particular time.

Basalt: A volcanic igneous rock which is dark in colour, fine grained and basic in composition and which was originally erupted as lava.

Basalt columns: A feature that forms during the cooling of a thick basaltic lava flow.  Joints or cracks form as a result of thermal contraction on cooling and form an extensive fracture network of hexagonal columns.

Basaltic Lava: A lava of iron and magnesium-rich composition, that has a low silica content and erupts at extremely high temperatures.  It flows readily across the surface.

Bauxite: The most common aluminium oxide which can be mined from a rock in order to make a profit.

Bivalves: A class of marine and freshwater molluscs.  Their shell consists of two asymmetrically rounded halves known as valves which are mirror images of each other and joined by a hinge at one end.

Blanket Bog: An area of peatland which forms over a large area in conditions of high rainfall and low levels of evapotranspiration.


Calcareous Mudstone: A mudstone that is mostly or partly composed of calcium carbonate.

Carboniferous: Geological time period extending from 354 million years ago to 290 million years ago.

Cenomanian Transgression: A marine transgression that occurred during the Cenomanian which is a division of the Upper Cretaceous.

Chalk: A soft, white, porous sedimentary rock – a form of limestone that is composed of the mineral calcite (calcium carbonate).  It forms in deep marine conditions as a result of the build up of the shells of microorganisms known as coccoliths.

Clasts: A rock fragment or grain that resulted due to the breaking down of larger rocks.  They can vary in size greatly, from millimetres to meters.

Clay: A naturally occurring material that is very fine grained and forms due to long periods of chemical weathering of silicate bearing rocks.

Coal: A sedimentary rock made up of nearly 100% organic carbon.  It is formed by the burying and compaction of swamp vegetation.

Coccolith: A microscopic marine algae with a calcareous outer shell.

Conglomerate: A sedimentary rock which is made up of fragments which range in shape and size.

Cretaceous: Geological time period after the Jurassic but before the Palaeogene, from approximately 142 million years ago to 65 million years ago.

Crinoids: Marine organisms that have been alive for millions of years.  Their fossil remains can be identified on the foreshore at Larne.


Dalradian: A term that represents metamorphic rocks associated with the opening and closing of the Iapetus Ocean.  They are mostly from 600 – 420 million years ago.

Desiccation cracks: A feature that form as a result of drying out.  They confirm environments which are hot and arid that experience periodic rainfall followed by periods of drying out.

Devonian: Period of geological time extending from 417 million years ago to 354 million years ago.  The Carboniferous is the time period after and the Silurian the time period before.

Dolerite: An igneous rock which is dark in colour, medium grained and basic in composition.  It has the same composition as basalt only coarser crystals due to the rate of cooling.

Dyke: Vertical (or nearly vertical) igneous intrusion that cuts up through older rocks.


Epoch: A subdivision of a geological time period.

Erosional Surface: A surface, or expanse, of rock that has been subjected to high amounts of erosion.  This means these sediments that were once deposited are now removed and so represent a time gap or unconformity.

Exposure: In geological terms, it refers to a rock being visible at the Earth’s surface.


Fault: A planar fracture within a volume of rock over which significant movement can occur.  It is a line of weakness that forms due to tectonic processes.

Fault Breccia: A breccia that was formed due to tectonic processes.  It is an unconsolidated rock composed of broken, fragmented rocks.

Flint: A rock type composed of microscopic crystalline silica.  It forms nodules within the Cretaceous Chalk.

Flood Basalts: A huge basaltic lava plateau which extends for kilometres in flat, layered flows.  It originates from fissures.

Folding: A deformation process that results deep within the Earth, at high temperatures and pressures.  It results in rocks that appear to have been bent.

Foraminifera: Microscopic (less than 1mm in size) marine organism that is both living and fossil.  They produce a test, or shell, of calcium carbonate.

Freeze-Thaw Action: A type of weathering process that operates when the temperature is around the freezing point of water.  It operates on the basis that water contracts when it thaws and expands when it freezes resulting in a change in volume.  Therefore water in pore spaces or fractures in rocks causes them to weaken and ultimately to break up.


Glauconite: A green mineral – a hydrous silicate of iron and potassium.  It indicates a marine environment.

Glauconitic sandstone: Sandstone with a green tinge due to the presence of the mineral Glauconite.

Glenarm Chalk Member: The eighth of fourteen members of the Ulster White Limestone formation deposited during the Cretaceous period 142 to 65 million years ago.  A formation is an important component within stratigraphy and can be further divided into members which can ultimately be grouped.


Hibernian Greensands Formation: A division of the Cretaceous rocks in Northern Ireland.  This formation is restricted to the south and eastern fringes of the Antrim Plateau.

Holocene: Geological epoch within the Quaternary period.  It encompasses the last 10,000 years.

Hornfels: A name of a group of contact metamorphosed rocks that have been baked by the heat of an igneous intrusion.  They are usually very hard and fine grained rocks.

Hummocky: A term applied to extremely irregular surfaces where there are many small mounds rising above the ground surface.


Iceland Plume: An upwelling of anomalously hot rock in the Earth’s mantle beneath Iceland.

Iron Ore: A metal bearing rock from which iron can be extracted.

Isostasy: A process that tries to restore to a state of gravitational equilibrium.  It operates due to the fact that the Earth is dynamic and so responds to the addition and removal of loads, such as ice.  When temperatures rise and ice melts the weight of the ice is removed from the surface of the Earth causing the Earth’s crust to gradually rise up; this is the process of isostasy.


Jurassic: Period of the stratigraphical column from approximately 206 million years ago to 142 million years ago.


Last Glacial Maximum: Refers to the time of maximum extent of ice sheets during the last glacial period which was approximately 20,000 years ago.

Laterite: A weathering product, commonly igneous rocks.  Generally occurs in wet tropical conditions and produces a reddy/brown sediment.

Lithology: The study of the physical characteristics of rocks.

Lias Clay: Lias is a term used in stratigraphy defining the lower part of the Jurassic Period.  It is characterised by grey clays and mudstones in northeast of Ireland.

Lignite: A soft brown fuel whose characteristics make it lie in between coal and peat.

Limestone: A sedimentary rock composed mainly of calcium carbonate in the form of the mineral calcite.

Lithosphere: The strong, rigid outer shell of the Earth that sits above the asthenosphere and encompasses the crust and the upper brittle part of the mantle.

Lower Basalt Formation: The term given to the first series of lavas that flowed across the region some 62 – 60 million years ago during the Palaeogene Period.


Magma: Molten rock that, when cooled, forms an igneous rock.  Magma that extrudes onto the surface is termed lava and magma that intruded below the surface and solidifies there forms intrusive igneous rocks.

Marine Transgression: A geological event whereby sea levels rise relative to the land surface causing the shoreline to move to higher ground.

Mercia Mudstone Group: A sequence of sedimentary rocks that occurs widely across Britain and Ireland. It consists of mudstones, siltstones and sandstones and is Triassic in age.

Mudstone: A sedimentary rock composed of clay size particles.  It is structureless and unlaminated.


Oil Shale: An organic rich, fine grained sedimentary rock that contains large amounts of kerogen from which liquid hydrocarbons can be extracted.

Old Red Sandstone: Continental sandstones that are part of the Devonian Period.

Olivine Basalt: A type of basalt that has an abundance of the mineral olivine.  Olivine is a yellow-green magnesium iron silicate mineral.

Ordovician: Geological time period approximately 495 million years ago to 443 million years ago.


Palaeogene: Geological time period which is part of the Cenozoic era, extending from 65 million years ago to 23 million years ago.

Palagonite: A clay alteration product that has been derived from the volcanic glass that formed when the hot lava chilled against the water

Pangaea: A supercontinent that was made of all the current continents.  It existed approximately 200 million years ago.

Permeable (Permeability): A measure of how porous a material is, i.e. the ability of a material to transmit water.

Permo-Triassic: Is a term used to describe a rock or event that is from both the Permian and Triassic Periods.

Pillow Lava: A type of lava that formed under water in which small pillow shaped tongues break through the surface and quickly solidify.

Porcellanite: So called due to its fine-grain blue appearance that looks like porcelain.  It forms by the heating of weathered basalt (laterite).  The heat comes from the neighbouring volcanic plug.

Precambrian: Time period of the stratigraphical column indicating the time from 4,600 million years ago to 545 million years ago.

Precipitation: The process by which a solid forms from a solution.

Psammite: A medium grained metamorphic rock that was originally sandstone.

Pyroclastic Deposit: (singular: pyroclast) A volcanic rock fragment that is ejected into the air during a volcanic eruption.


Quaternary: Period of the stratigraphical column extending from approximately 2.6 million years ago to the present.


Raised Beaches: Coastal beaches and other formations such as cliffs and caves that are above the present shore line.  They formed after the Ice Age when the sea level was higher due to melting of the ice.

Recent: The name given to the time period we live in today.  It is the final epoch of the Quaternary Period and is also known as the Holocene.

Recharge: A hydrologic process whereby water fills up stores such as the soil.  When the amount of precipitation (recharge) exceeds the rate of infiltration water will appear on the surface i.e. the stores will be ‘recharged’.

Red Arch Formation: A formation dated as Upper Devonian which consists of unfossiliferous conglomerate and pebbly sandstone and can be spilt up into 5 different units.  It is commonly found at Cushendall and sits in unconformable contact above Lower Devonian rocks of the Cross Slieve Group.

Rifting: Faulting as a result of thinning and stretching of the crust that results in large amounts of volcanism and a new ocean forming in the space created.

Rip Current Channels: A rip current is a strong channel of water that flows seaward from the near shore.

Rotational Slip: The slipping of a rock unit along a curved plane on a decline.


Sandstone: A sedimentary rock composed of cemented sand grains.  Its grain size can vary.

Schists: A metamorphic rock which has been subjected to high temperatures and pressures deep within the earth.  It is characterised by its shiny appearance due to the formation of secondary mica.

Scree Slope: Accumulation of broken rock fragments on a slope.

Sea Caves: A cave formed primarily by the wave action of the sea.

Shale: A fine grained sedimentary rock which is made up of both silt and clay.

Sill: Horizontal (or near horizontal) body of igneous rock that has been intruded into older sediments in which it lies conformably.

Silurian: Time period extending from 443 million years ago to 417 million years ago.

Solution Hollows: A natural depression on the Earth’s Surface formed due to the chemical dissolution of carbonate rocks.

Speleothems: Speleothems are cave formations that commonly form in limestone caves.

Stable Dune System: A hill composed of sand formed by aeolian processes.  Its condition is described as stable when it is neither growing nor depleting.

Stacks: A geological landform consisting of columns of rock in the sea or by the coast that have been isolated due to erosional processes such as wave action.

Stalactites: A type of speleothem that hangs from the ceiling in limestone caves.  It is composed of calcium carbonate.

Stalagmites: A type of speleothem that rises up from the floor of a limestone cave. It forms from calcium carbonate rich solution dripping down from the roof of the cave. If a stalagmite meets a stalactite they form a column.

Stratigraphy: The study of strata or layers within geology.

Succession: A stratigraphical term used to describe a vertical set of rock strata.  It is used to provide a chronological record of the geological history of the area.


Terrestrial Sediment: Sediments gathered from land above the tidal reach.

Tombolo: A bar that extends outward from the shore, connecting with an island.

Triassic: Time period extending from 248 million years ago to 206 million years ago.

Tuff: A rock that is made up of compacted volcanic debris such as volcanic ash.

Tundra: A biome where tree growth is hindered by low temperatures and a short growing season.  There are three types; Arctic tundra, Alpine tundra and Antarctic tundra.


Ulster White Limestone Formation: Also known as chalk, was deposited in the Cretaceous approximately 142 million years ago.

Unconformity: A surface of erosion or non-deposition that separates younger rocks from older rocks.  It represents the passage of time.

Upper Basalt Formation: The termed given to the second cycle of lavas that flowed across the region during the Palaeogene 65 million years ago to 23 million years ago.


Vesicles: A small, usually spherical, gas cavity.  Occurs in volcanic rocks and represents gas escape.

Volcanic Ash: A material which is expelled from an active volcano during its eruption.  If it becomes compacted it turns into a rock known as Tuff.

Volcanic Vent: A volcanic opening, sometimes a pipe, which can often be filled with fragmental material.

Volcanic Plug: A volcanic landform formed when magma hardens within a volcanic vent of an active volcano.


Waterloo Mudstone Formation: Also known as Lias Clay, it was deposited in the Jurassic approximately 200 million years ago.

Wave Cut Platform: A level surface, or platform, formed by the erosive power of waves, in coastal bedrock, e.g. cliffs.