Glossary

Words in bold italic are defined elsewhere in the glossary.

accretionary prism Wedge of material built up by underthrusting of successive slices of sediment on the landward side of a subduction zone.

acritarch Marine, hollow, organic walled microfossil of uncertain affinities.

adit More or less horizontal tunnel to mine.

agglomerate Conglomerate or breccia of volcanic origin.

aggradation Accumulation of sediment resulting in raising of the substrate.

alga (pl. algae) Primitive plant-like organism. Some may secrete calcium carbonate and algal mats may play a role in sediment accumulation in some environments. See stromatolite.

amygdale Cavity within a lava, dyke or sill, lined or filled with secondary minerals.

andesite Fine-grained volcanic rock of intermediate composition (with about 53-60% silica).

anhydrite CaSO₄ White to grey, rock-forming evaporite mineral. ankerite Ca(Fe,Mg,Mn)(CO₃)₂ Mineral, may be crystalline of various colours but often yellowish-brown, massive or granular, commonly replacing the wallrock of Pennine veins.

anticline See fold.

apatite Fluophosphate or chlorophosphate of calcium.

Characteristically green or grey-green mineral in hexagonal prisms. Found in igneous and metamorphic rocks, and principal mineral of fossil bone.

aplite Pinkish, fine-grained quartz-alkali feldspar rock associated with granite and usually occurring in veins.

arenite Sedimentary rock of sand-grade with <15% mud matrix (hence arenaceous).

argillaceous Silt to clay grade sediments (grains <0.0625 mm diameter).

arkose Sand-grade rock containing 25% or more feldspar.

autobreccia Rock broken into angular fragments by internal processes. Usually applied to a lava crust brecciated by continuing movement within the flow hence autobrecciation.

back-arc basin Sedimentary basin formed behind a volcanic island arc, above a subduction zone.

baryte/barytes BaSO₄ Baryte is a colourless to white mineral, commonly in tabular crystals, noticeably heavy. A common gangue mineral. Barytes is the commercial product.

basalt Dark, often almost black, fine-grained basic volcanic rock, low in silica (no quartz) and relatively rich in iron, magnesium and calcium.

bioclast A shell or skeletal fragment.

biomicrite A micritic (mud-grade) limestone containing bioclasts.

biostrome Sheet-like accumulation of fossil shells or skeletons.

biotite Common, dark brown to black, Mg, Fe-rich mica.

bioturbation Reworking of unconsolidated sediment by burrowing organisms which may partly or completely destroy primary structures (i.e. bedding); hence bioturbated.

bismuthinite Bi2S3 Soft, greyish-white mineral, commonly in bladed crystals.

bivalve Marine to fresh-water mollusc in which the plane of symmetry of the bi-valved calcium carbonate shell is the plane of opening of the two valves (as in cockles or mussels).

Bouma sequence Idealized sequence of sedimentary structures found within a turbidite bed, from base: massive or graded sand; lower parallel lamination; ripple lamination; upper parallel lamination; pelagic shale.

B.P. Years before present (conventionally taken to be 1950).

brachiopod Solitary marine animal with bi-valved calcite shell. The plane of symmetry is perpendicular to the plane of opening of the valves.

breccia Coarse elastic rock in which the clasts are angular. See also fault.

bryozoa Small colonial animals with a calcite skeleton consisting of large numbers of tiny tubular or box-like chambers. Colonial form very variable.

calcite CaCO₃ Colourless or white mineral which is the main constituent oflimestone. Crystals when formed (i.e. in veins) may be tabular or prismatic.

calcrete Nodular or massive, laminar carbonate bed formed in a soil in semi-arid regions.

Caledonian Mountains/Orogeny See orogeny.

carbonate rocks Limestones or dolostones (dolomites).

cassiterite SnO₂ Hard, heavy, usually reddish-brown to black mineral, massive or with pyramidal or prismatic crystals. In Northumbria, known only as minute inclusions in other vein minerals.

cataclastic Formed by shearing and granulation as a result of tectonic movement.

cementstone General term for extremely hard carbonate-rich bed capable of being ground as cement.

chalcedony SiO₂ White or greyish-white, fibrous to cryptocrystalline, stalactitic or botryoidal quartz.

chalcopyrite CuFeS₂ (copper pyrites) Brass-yellow mineral commonly with an iridescent tarnish. Most common copper mineral. Crystals usually tetrahedra.

chert Nodules, lenses or impersistent bands of cryptocrystalline quartz, usually black, grey or red in colour, usually of diagenetic origin in sedimentary sequences.

chlorite (Mg,Fe)₅Al(AlSi₃)O₁₀ Soft, green, platy mineral associated with low-grade metamorphism. Found also in amygdales and veins.

chute A downslope, sub-glacial meltwater channel.

clast Rock fragment; hence clastic rock. The principal elastic rocks are distinguished on grain size thus: conglomerate > 2 mm > sandstone > 0.0625 mm siltstones > 0.004. mm>mudstone/shale.

cleavage A close-spaced, regular fracture or fabric imposed on strongly folded beds and best developed in weaker, fine-grained rocks. Perfect cleavage is parallel to the axial plane of a fold.

cone-in-cone Fabric of adjacent sets ofvertically nested cones, each about 3 cm or more in diameter, caused by precipitation of CaCO₃ under pressure in a mud-grade rock.

concretion Spherical or ellipsoidal, more resistant mass formed by local early cementation of the sediment. They often occur regularly or irregularly spaced in layers and weather out of the softer surrounding sediment.

conformable Sequence of rocks in apparently continuous succession. conglomerate Coarse clastic rock in which the clasts are rounded. An intraformational conglomerate is one formed of locally derived clasts from a recently deposited source.

coral A polyp or polyps (anemone-like) with a basal skeleton of calcium carbonate. Corals may be solitary or colonial, the latter varying from flat, tabular masses to clusters of branching tubes.

crevasse Breach in a river bank or levee through which sediment-charged water may flow to form a crevasse-splay deposit.

crinoid (sea lily; feather star) Marine organism (echinoderm) with a plated cup, showing radio-pentameral symmetry and bearing feeding arms, supported in sea lilies by a stalk. The disc-shaped ossicles or columnals of the stalk are a major constituent of Palaeozoic limestones, hence crinoidal limestone.

cross-stratification, cross-bedding, cross-lamination Sedimentary structure in which the migration of the slip face of ripples, dunes or bars produces a series of inclined laminae (foresets) between sub-horizontal bedding surfaces. Different types are planar, when the laminae are flat, trough, when the laminae are scoop-shaped and hummocky, when individual sets of cross-beds cut across each other leaving hummocky bounding surfaces.

cyclothem A particular sequence of beds repeated again and again in vertical succession. Particularly notable in the Carboniferous (see Yoredale).

dacite Light-coloured, fine grained, volcanic rock of acid– intermediate composition.

deflation Erosion of land surfaces through the agency of wind.

diagenesis The changes that take place in the conversion of a sediment to a rock.

diopside CaMgSi₂O₆ Pale, dirty green or grey silicate mineral of the pyroxene group, common in more basic igneous rocks. May form short prismatic crystals.

dip The maximum angle of inclination of a planar surface, usually bedding. Measured in the vertical plane at right angles to the strike. dolerite Dark coloured, medium-grained igneous rock of basaltic composition.

dolomite CaMg(CO₃)₂ White, colourless, yellowish or brown mineral; rhombic crystals with curved faces. Term also used for the characteristically browny-yellow rock composed mainly of the mineral, but more correctly termed dolostone.

downthrow See throw.

draa A large sand ridge or dune chain, the largest desert landform.

drift Any superficial, unconsolidated sediments of the Quaternary.

drumlin Smooth, streamlined, oval mound of till (boulder clay), usually in groups (drumlin field or swarm), formed beneath an advancing ice sheet. The long axis of the drumlin is parallel to the direction of advance.

dyke More or less vertical, cross-cutting intrusion. May exist en echelon, as discrete, overlapping or more distant, offset elements (echelons).

echelon See dyke.

echinoid (sea urchin) Marine invertebrate with body enclosed in a globular or discoidal test. Symmetry either pentameral radial (regular echinoids) or pentameral bilateral (irregular, burrowing, echinoids).

epidote Ca₂(A1,Fe)₃(SiO₄)₂OH Characteristically green, radial, fibrous or columnar mineral, sometimes forming prismatic crystals, associated with hydrothermal or contact metamorphic rocks.

erratic Glacially transported rock derived from outside the local area.

esker Long, sinuous, steep-sided ridge consisting ofsands and gravels, formed either in an englacial tunnel or at the edge of a retreating ice sheet.

eustatic World-wide change in sea level.

euxinic Environment with little or no oxygen, and sediments formed therein.

evaporite Rocks or minerals formed by precipitation ofsalts from natural brines by evaporation.

facies Features of a rock or rock sequence that reflect the environment of deposition.

facing Direction in which beds in a fold hinge become younger.

fault A more or less planar fracture in a rock mass along which relative displacement of adjacent blocks has occurred. The face of the block above an inclined fault plane is the hanging wall, that below is the footwall. In most faults, the direction of movement is known or assumed to be predominantly vertical. In a strike-slip or wrench fault, the direction of movement on a sub-vertical plane is predominantly horizontal. A thrust fault has a sub-horizontal plane of displacement. Fractured rock on the fault plane caused by movement between adjacent blocks is a fault breccia.

feldspars Important group of rock-forming silicate minerals, common in igneous rocks, hence feldspathic.  Alkali feldspar is K– Na series feldspar. Plagioclase is Na–Ca series feldspar, often forming white, lath-shaped phenocrysts in igneous rocks. Most feldspars break down quickly on weathering.

fireclay See seatearth.

flat A lenticular zone of mineralization parallel to bedding.

flaser bedding Ripple bedding with silt or clay drapes between sets.

fluorite CaF₂ Colourless to translucent, purple, green or yellow mineral commonly crystallising in cubes. Fluorspar is the commercial product.

flute cast (flute mark) See sole structure.

fold A bend in bedded rocks or any planar rock mass. An anticline is arched upwards with older rocks in the core. A pericline is an anticline in the form of an elongated dome. A syncline is bent downwards with younger rocks in the core. A monocline is a step-shaped fold, with one steep limb between two hinges. An isoclinal fold has subparallel fold limbs. The dip of the fold axis is the plunge of the fold.

foraminifera Microscopic single-celled organism with a chambered, usually calcium carbonate, test.

foresets See cross-stratification.

galena PbS Lead grey mineral crystallizing in cubes and octahedra. The main ore of lead.

gangue Non-metallic mineral (i.e. quartz, fluorite, baryte) in veins with which ore minerals are associated. Formerly of no commercial value, fluorite and baryte are now important products.

ganister See seatearth.

garnet Group of Ca, Fe, Mg, Mn silicate minerals ofvariable composition, often deep reddish-brown in colour, found in igneous and metamorphic rocks.

gastropod Mollusc with a usually helically coiled calcium carbonate shell (snail) or naked (slug).

glacioeustatic Eustatic changes in sea level resulting from growth or decay of an ice sheet.

glaciofluvial Sediments or landforms produced by meltwater from a glacier.

glaciogenic Of glacial origin.

gley Waterlogged, anaerobic soil.

gneiss Coarse-grained, banded rock formed under high-grade metamorphic conditions.

graben A linear tract of country, lowered between two bounding faults. A half-graben is fault-bounded on one side only.

graptolite Extinct group of marine, pelagic, colonial organisms with an organic skeleton. Individuals a few mm long, colonies t o's mm long. Usually preserved as a carbonaceous film.

granite A coarse-grained acid igneous rock containing quartz, alkali feldspar and mica.

granodiorite A coarse-grained acid–intermediate igneous rock containing quartz and dominant plagioclase feldspar.

granophyre A granite characterized by fine-scale intergrowths of quartz and feldspar.

greywacke A poorly sorted (immature) silt-sand grade clastic rock with >15% clay-grade material.

gypsum CaSO₄.2H₂O Evaporite mineral, usually white, finely granular or massive. A transparent variety (selenite) may be precipitated within sediments under some conditions. The fibrous form (satin spar) may form veins.

haematite Fe₂O₃ Steel-grey to black, sometimes red mineral, occurring as tabular crystals or massive, often botryoidal.

half-graben See graben.

halite (rock salt) NaCl Common salt, an evaporite mineral, usually white, crystals usually cubes.

hanging wall See fault.

hornblende Green or brown rock-forming silicate mineral of the amphibole group, characterised by two cleavages intersecting at 124°. hornfels Massive hardened, splintery rock formed by alteration of the country rock by contact (thermal) metamorphism.

hummocky cross-stratification See cross-stratification.

hush Opencast workings or trials excavated in part by releasing torrents of water from reservoirs high on a hillside. Large examples may be difficult to distinguish from natural valleys.

hydrothermal Associated with the action of hot water.

imbrication More or less parallel orientation of platy/tabular clasts, generally sloping up-current and thus indicating the direction ofwater flow.

igneous Rocks crystallized or solidified from a molten state. May be divided into basic (45-53% silica), intermediate (53-60% silica), and acid (>60% silica, including free quartz).

inlier Area of older rocks surrounded by younger rocks.

intermontane basin Sedimentary basin being infilled from erosion of surrounding mountains.

intraclast Fragment derived from the erosion of a nearby sediment and redeposited within the same area.

isoclinal See fold.

jarosite KFe₃(SO₄)₂(OH)₆ Yellowish-brown, usually earthy mineral of secondary origin.

joint Fracture in rock along which little or no movement can be detected. Usually they occur in more or less regularly spaced sets, and two or more sets may intersect at various angles. As well as tectonic joints, they may form through cooling (igneous rocks) or shrinkage in a sediment.

kame Steep sided mound of bedded glaciofluvial sand and gravel associated with stagnant ice. A kame terrace is a continuous linear feature formed between an ice mass and a valley wall. Subsequent ice melt may result in signs of marginal slumping.

kettle hole Depression in glacial drift, possibly containing a lake, left by the melting of an included mass ofice.

laccolith Concordant, lenticular, igneous intrusion, elliptical or circular in plan.

lacustrine Sediment or processes associated with lakes.

lag An accumulation of coarse clastic or bioclastic material, usually in the floor ofa channel.

limonite A general term for unspecified hydrous earthy iron oxides usually derived from the weathering ofiron minerals in rocks or veins. linguoid Tongue-shaped (of asymmetrical ripples).

lithology Physical features ofa rock. Hence lithostratigraphy, the statigraphic ordering ofdifferent rock types; lithification, process of turning unconsolidated sediment into rock.

Ma Abbreviation for 'million years'.

magma A hot, liquid or semi-liquid melt within the Earth's crust; the source for all igneous rocks and processes.

marcasite FeS₂ Pale brass-yellow or greyish metallic mineral, common as bladed or laminated crystalline masses in Pennine veins.

marl A calcareous clay with 35-65% soft calcium carbonate.

meltwater channel Channel cut by the action of meltwater from a glacier or from snow. Usually unrelated to the present drainage pattern.

metamorphic Rock formed by the alteration of a pre-existing rock by changes in temperature and/or pressure.

metasediment A metamorphosed sediment.

mica A group of complex silicate minerals characterised by a strongly platy habit.

micrite Microcrystalline calcite (lime mud).

microgranite A medium-grained (1-5 mm) rock ofgranitic composition.

mineral veins See veins.

mollusc One of a very diverse invertebrate group including the bivalves, gastropods, and cephalopods (nautiloids, etc.)

monocline See fold.

moraine An unsorted deposit of rock debris associated with the actions of a glacier.

nautiloid Cephalopod mollusc with a curved or straight, tapering, chambered shell; suture simple, siphuncular tube central in chambers.

olivine A group of olive green to brown or black rock-forming Mg, Fe silicate minerals, characteristic ofsilica-poor igneous rocks.

oncolite Spherical or sub-spherical particle up to 50 mm diameter formed by the action of algae in trapping sediment on the surface ofa mobile grain.

oolite Rock formed largely of ooliths. Characteristic ofhigh-energy, shallow-water environments.

oolith Spherical or sub-spherical particle less than 2 mm diameter formed by the concentric deposition ofrings of (usually) calcium carbonate around a mobile grain.

orogeny Process of mountain building by the lateral compression of thick rock sequences. The Caledonian Orogenic Cycle refers to a series of orogenic events in the Lower Palaeozoic culminating in the late Silurian/early Devonian. The Variscan Orogeny, whose main effects are seen in southwest England and Central Europe, spanned the late Devonian to late Carboniferous.

ostracode Small to microscopic, marine to fresh-water crustacean with calcitic bivalved shell.

outlier Area ofyounger rocks surrounded by older rocks.

overflow channel, spillway Channel carved by the overflow from an ice-dammed lake. Usually unrelated to the present drainage pattern.

overstep Relationship where a bed deposited by a transgression rests on the eroded ends of several beds below the plane of unconformity.

palaeosol Fossil soil.

pedogenic Associated with soil formation.

pericline See fold.

phenocryst Larger, usually well-formed crystal in a finer groundmass. phonolite Fine grained, porphyritic, Na-rich volcanic rock. phytoplankton See plankton.

plankton Mainly small to microscopic organisms that float in near-surface oceanic waters; divided into phytoplankton (photosynthetic) and zooplankton (animals).

plate A part of the Earth's rigid outer shell (lithosphere), internally relatively free of earthquakes and volcanic activity but bounded by more or less continuous zones of earthquakes and volcanoes where the plates move against each other.

Plate tectonics describes the processes and effects of plate motions and interactions.

plunge See fold.

pluton A large igneous intrusion (excluding dykes and sills).

post A bed of rock, often applied to limestones.

progradation The outward extension of a sedimentary deposit, such as a delta building out from a shoreline.

pseudomorph Retention of the original crystal form after a mineral has been replaced.

pyrite FeS₂ (fools gold) Common pale brass-yellow mineral, often crystallising in cubes.

pyroclastic A clastic rock of volcanic origin.

pyroxene Important group of dark green, brown or black, rock-forming silicate minerals, characterised by two cleavages at right-angles; crystals prismatic.

pyrrhotite (magnetic pyrites) FeS Bronze-yellow, reddish-brown weathering, usually massive or granular mineral; magnetic.

quartz SiO₂ Very common mineral, usually transparent or white but may be variously coloured. Occurs in many igneous and metamorphic rocks, is the main constituent of sandstones and siltstones and a common gangue mineral in veins when prismatic crystals with a six-faced pyramidal termination may be found.

regression Withdrawal of the sea from the land area due to a relative fall in sea level.

rhyolite Fine-grained acid igneous extrusive rock; volcanic equivalent ofgranite.

rock-salt See halite.

schist A metamorphic rock with a strong, platy fabric, caused by the parallel alignment of micas.

seafloor spreading Process whereby volcanic activity at mid-ocean ridges causes igneous rock material to be accreted to plate margins resulting in the growth of oceanic crust.

seatearth A fossil soil with root traces found immediately below a coal

seam. A fireclay is a pure clay seatearth, whilst a ganister is a pure quartz sand seatearth.

septarian Nodules or concretions with a series of internal mineral-filled (usually calcite) cracks. Results from the formation of a hardened exterior shell before desiccation and shrinkage of the material inside the nodule.

serpulid A group of polychaete worms with calcareous tubes. sheath fold A highly deformed fold form with a strongly curved fold axis, produced in shear zones.

siderite FeCO₃ Grey to grey-brown mineral widespread in certain sedimentary rocks, particularly sedimentary ironstone deposits and Coal Measures sequences. Also common in many Pennine veins.

siliciclastic Clastic rocks formed predominantly of quartz, other silicate mineral and rock fragments.

sill A tabular igneous intrusion, mainly concordant with bedding, although it may cut across beds from one level to another. slickensides A lineation on a fault or bedding plane caused by the relative movement of rock masses on either side. The surface is often coated by fibrous crystals, usually of quartz or calcite, aligned in the direction of movement.

sole mark/structure Sedimentary structure cut into an underlying mud by a turbidity current and infilled by the overlying turbidite bed. Preserved as a cast on the base of the turbidite. Flute cast (mark): ovoid scoop-shaped structure caused by turbulent water flow, preserved as a tapered lobe on the base of the turbidite. Sole marks may also occur less typically in fluvial sediments, etc.

solifluction Downhill movement of surface layer ofunconsolidated weathered material when saturated by water.

sphalerite (blende) ZnS Commonly a brown or black mineral with a resinous lustre and variable form. Most common ore ofzinc.

spillway 1. General term for glacial meltwater or overflow channels. 2. Overflow channel constructed on a dam.

sponge Primitive invertebrates with an asymmetrical body supported by spongin and/or siliceous or calcareous spicules. Some may have a massive calcareous basal skeleton.

S.S.S.I. Site of Special Scientific Interest.

stadial A period of increased cold or advancing ice.

stope Underground excavation in a vein.

strike Intersection ofa bedding plane, or other planar surface, with the horizontal.

strike-slip See fault.

stromatolite A carbonate rock with a fine horizontal, domal or columnar banding, reflecting the control ofdeposition by an algal mat or microbial community living on the surface of the sediment.

stylolite An irregular, suture like contact, most common in limestones, produced by solution of the rock under high pressure.

subduction The process whereby oceanic crust descends into the interior of the Earth beneath oceanic or continental crust at a convergent plate margin.

suture 1. A linear zone ofcontinental collision, marking the site ofa former ocean. 2. Line ofjunction of septum with conch wall in cephalopods.

syncline See fold.

tachylite Black, glassy rock formed by chilling of a basaltic lava or shallow igneous intrusion.

tectonic Relating to deformation of rock masses, as in mountain-building episodes.

tholeiitic basalt/dolerite A type of basalt/ dolerite oversaturated in silica, so that small amounts of quartz are present.

throw Description of vertical component of movement on afault plane. Downthrow emphasises the relative downward displacement ofa block on one side of the fault, upthrow (less commonly used) emphasises the relative upward displacement of a block.

thrust See fault.

till (boulder clay) Collective term for the group of unsorted sediments laid down by direct action ofice.

tourmaline A group of complex boro-silicate minerals, normally black or bluish-black; prismatic crystals with a typical triangular cross-section.

trace fossil A structure resulting from the activity of an animal, such as a burrow or a grazing trail.

transgression 1. An advance of the sea over the land, caused by a relative rise in sea level. 2. Change of stratigraphic level by a sill.

tremolite Ca₂(Mg,Fe)SiO₈O₂₂(OH)₂ White or greyish-white mineral with needle-like crystals.

trilobite Extinct group of arthropods, with a dorsal skeleton divided into head (cephalon), thorax and tailplate (pygidium).

tufa Rock formed by the depositon of calcium carbonate (more rarely silica) as a sometime porous and/or banded mass around saline springs, or associated with stalactites and stalagmites.

tuff Lithified volcanic ash-fall.

turbidite Rock deposited from a turbidity current/flow, a fast flowing turbulent current charged with a high sediment load, commonly initiated by the disturbance ofsoft sediment on a slope. A turbidite is poorly sorted but may show grading and sole structures on its base.

unconformity Surface of contact between two groups of rocks resulting from the tilting or folding and erosion of the lower group (often in an orogenic event) before the deposition of the upper group.

Variscan Orogeny See orogeny.

vein/veinlet A fracture, usually sub-vertical, which is mineralized, often with quartz or calcite. Crystals may grow from the walls towards the centre. A mineral vein normally implies the presence of ore minerals.

volcaniclastic A clastic rock of volcanic origin.

witherite BaCO₃ A white, pale creamish white or grey mineral, crystals six-sided prisms and pyramids. Notably heavy.

xenolith An inclusion of country rock within an igneous body.

Yoredale Name applied to repeat cycles oflimestone-shale-sandstone (-seatearth-coal) (cyclothems) in the Carboniferous (Dinantian, early Namurian), derived from the old name for Wensleydale, where they are typically developed.