The Whin Sill or Great Whin Sill is a tabular layer of the

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

rock

dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained ...

County Durham County Durham ( ), officially simply Durham,UK General Acts 1997 c. 23Lieutenancies Act 1997 Schedule 1(3). From legislation.gov.uk, retrieved 6 April 2022. is a ceremonial county in North East England.North East Assembly �About North East E ...

Northumberland Northumberland () is a county in Northern England, one of two counties in England which border with Scotland. Notable landmarks in the county include Alnwick Castle, Bamburgh Castle, Hadrian's Wall and Hexham Abbey. It is bordered by land on ...

and

Cumbria Cumbria ( ) is a ceremonial and non-metropolitan county in North West England, bordering Scotland. The county and Cumbria County Council, its local government, came into existence in 1974 after the passage of the Local Government Act 1972. Cumb ...

in the northeast of

England England is a country that is part of the United Kingdom. It shares land borders with Wales to its west and Scotland to its north. The Irish Sea lies northwest and the Celtic Sea to the southwest. It is separated from continental Europe b ...

. It lies partly in the

North Pennines The North Pennines is the northernmost section of the Pennine range of hills which runs north–south through northern England. It lies between Carlisle to the west and Darlington to the east. It is bounded to the north by the Tyne Valley and ...

Area of Outstanding Natural Beauty An Area of Outstanding Natural Beauty (AONB; , AHNE) is an area of countryside in England, Wales, and Northern Ireland, that has been designated for conservation due to its significant landscape value. Areas are designated in recognition of thei ...

and partly in

Northumberland National Park Northumberland National Park is the northernmost national park in England. It covers an area of more than between the Scottish border in the north to just south of Hadrian's Wall, and it is one of least visited of the National Parks. The park ...

and stretches from

Teesdale Teesdale is a dale, or valley, in Northern England. The dale is in the River Tees’s drainage basin, most water flows stem from or converge into said river, including the Skerne and Leven. Upper Teesdale, more commonly just Teesdale, falls ...

northwards towards Berwick. It is one of the key natural features of the

. A major outcrop is at the

High Force High Force is a waterfall on the River Tees, near Middleton-in-Teesdale, Teesdale, England. The waterfall is within the North Pennines Area of Outstanding Natural Beauty (AONB) and the European Geopark. The waterfall is part of the historic coun ...

waterfall in

Bamburgh Castle Bamburgh Castle is a castle on the northeast coast of England, by the village of Bamburgh in Northumberland. It is a Grade I listed building. The site was originally the location of a Celtic Brittonic fort known as ''Din Guarie'' and may have ...

Dunstanburgh Castle Dunstanburgh Castle is a 14th-century fortification on the coast of Northumberland in northern England, between the villages of Craster and Embleton. The castle was built by Earl Thomas of Lancaster between 1313 and 1322, taking advantage of t ...

Lindisfarne Castle Lindisfarne Castle is a 16th-century castle located on Holy Island, near Berwick-upon-Tweed, Northumberland, England, much altered by Sir Edwin Lutyens in 1901. The island is accessible from the mainland at low tide by means of a causeway. His ...

and stretches of

Hadrian's Wall Hadrian's Wall ( la, Vallum Aelium), also known as the Roman Wall, Picts' Wall, or ''Vallum Hadriani'' in Latin, is a former defensive fortification of the Roman province of Britannia, begun in AD 122 in the reign of the Emperor Hadrian. R ...

all strategically take advantage of high, rocky cliff lines formed by the sill. The Whin Sill complex is usually divided into three components:

Holy Island Sill Sacred describes something that is dedicated or set apart for the service or worship of a deity; is considered worthy of spiritual respect or devotion; or inspires awe or reverence among believers. The property is often ascribed to objects ( ...

, Alnwick Sill and the Hadrian's Wall-Pennines Sill, which were created by separate

magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma is found beneath the surface of the Earth, and evidence of magmatism has also been discovered on other terrestrial planets and some natural sa ...

flows, but at about the same time. The

Little Whin Sill Little is a synonym for small size and may refer to: Arts and entertainment * ''Little'' (album), 1990 debut album of Vic Chesnutt * ''Little'' (film), 2019 American comedy film *The Littles, a series of children's novels by American author John P ...

is an associated formation to the south, in

Weardale Weardale is a dale, or valley, on the east side of the Pennines in County Durham, England. Large parts of Weardale fall within the North Pennines Area of Outstanding Natural Beauty (AONB) – the second-largest AONB in England and Wales. T ...

Derivation of name

Much of the early study of geology began in the British Isles, whence much of the terminology is derived. Quarrymen of Northern England used the term 'sill' to describe a more or less horizontal body of rock. 'Whin' was applied to dark, hard rocks. As the intrusive igneous origin of the Whin Sill was determined in the 19th century, the term ' sill' was adopted by geologists for concordant, tabular intrusive bodies.

Geology

Towards the close of

Carboniferous Period The Carboniferous ( ) is a Period (geology), geologic period and System (stratigraphy), system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago (Myr, Mya), to the beginning of the Permian Period, ...

and in the early

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleoz ...

, some 295 million years ago (Ma), crustal extension caused by movement of the Earth's

tectonic plate Plate tectonics (from the la, label=Late Latin, tectonicus, from the grc, τεκτονικός, lit=pertaining to building) is the generally accepted scientific theory that considers the Earth's lithosphere to comprise a number of large te ...

s during the

Variscan orogeny The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Variscan'', comes f ...

allowed the emplacement of

igneous intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s of

across much of northern England of a suite of

tholeiitic The tholeiitic magma series is one of two main magma series in subalkaline igneous rocks, the other being the calc-alkaline series. A magma series is a chemically distinct range of magma compositions that describes the evolution of a mafic magma i ...

intrusion In geology, an igneous intrusion (or intrusive body or simply intrusion) is a body of intrusive igneous rock that forms by crystallization of magma slowly cooling below the surface of the Earth. Intrusions have a wide variety of forms and com ...

s. These were largely concordant with the

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as ei ...

of the existing

country rock Country rock is a genre of music which fuses rock and country. It was developed by rock musicians who began to record country-flavored records in the late 1960s and early 1970s. These musicians recorded rock records using country themes, vocal s ...

. On cooling, these crystallised and solidified to form the Great Whin Sill. It is dated at around 301- 294 million years old, thus spanning the Carboniferous/Permian boundary at 299 Ma. It underlies much of south and east Northumberland and the

Durham Coalfield The Durham Coalfield is a coalfield in north-east England. It is continuous with the Northumberland Coalfield to its north. It extends from Bishop Auckland in the south to the boundary with the county of Northumberland along the River Tyne in the ...

. Its maximum known thickness of around 70 metres occurs in the North Pennines. Surface and subsurface records of the Great Whin reveal it is not always concordant over wide areas and often rises and falls in the stratigraphical succession in marked leaps and gentle transgressions different levels. Studies of the

petrology Petrology () is the branch of geology that studies rocks and the conditions under which they form. Petrology has three subdivisions: igneous, metamorphic, and sedimentary petrology. Igneous and metamorphic petrology are commonly taught together ...

of the dolerites of the Whin Sill complex have revealed significant differences between the ''Little Whin Sill'' and the ''Great Whin Sill''. The Little Whin Sill is

olivine The mineral olivine () is a magnesium iron silicate with the chemical formula . It is a type of nesosilicate or orthosilicate. The primary component of the Earth's upper mantle, it is a common mineral in Earth's subsurface, but weathers quickl ...

-bearing and believed to be composed of an early differentiate of the Whin dolerite magma. On the other hand, the Great Whin, non-olivine-bearing and slightly density graded, is a later differentiate of the Whin magma. Two separate periods of Whin dolerite injection are confirmed by studies of

vitrinite Vitrinite is one of the primary components of coals and most sedimentary kerogens. Vitrinite is a type of maceral, where "macerals" are organic components of coal analogous to the "minerals" of rocks. Vitrinite has a shiny appearance resembling gla ...

reflectance over the

Alston Block The Alston Block is a term used by geologists to describe the geological structure of the North Pennines of northern England and which forms a part of the Pennine Block & Basin Province which originated during the Carboniferous period. It is defin ...

where two periods of Whin

contact metamorphism Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...

have been recognized. The two periods of Whin dolerite emplacement form part of the end-Carboniferous earth movements in northern England. They can be shown to have occurred between a period of compression from a W-SW direction and later gentle doming of the Alston Block near the Westphalian-Stephanian boundary, dated about 300–295 Ma. The

lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

is notable in many respects, including well developed

pegmatite A pegmatite is an igneous rock showing a very coarse texture, with large interlocking crystals usually greater in size than and sometimes greater than . Most pegmatites are composed of quartz, feldspar, and mica, having a similar silicic com ...

segregations which can be found in Upper Teesdale. Late stage

hydrothermal Hydrothermal circulation in its most general sense is the circulation of hot water (Ancient Greek ὕδωρ, ''water'',Liddell, H.G. & Scott, R. (1940). ''A Greek-English Lexicon. revised and augmented throughout by Sir Henry Stuart Jones. with th ...

mineralisation has filled the joints with

pectolite Pectolite is a white to gray mineral, sodium, Nacalcium, Ca2silicon, Si3oxygen, O8(Ohydrogen, H), sodium calcium hydroxide inosilicate. It crystallizes in the triclinic system typically occurring in radiated or fibrous crystalline masses. It has a ...

. The dolerite has been carbonated as

metasomatic Metasomatism (from the Greek μετά ''metá'' "change" and σῶμα ''sôma'' "body") is the chemical alteration of a rock by hydrothermal and other fluids. It is the replacement of one rock by another of different mineralogical and chemical com ...

selvages into veins and joints and other flaws to produce 'White Whin'. Thermal metamorphism of the country rock in the contact zone produced coarse grained

marble Marble is a metamorphic rock composed of recrystallized carbonate minerals, most commonly calcite or Dolomite (mineral), dolomite. Marble is typically not Foliation (geology), foliated (layered), although there are exceptions. In geology, the ...

s within the

contact aureole Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of chem ...

in a small number of places in Teesdale. Disused roadstone

quarries A quarry is a type of open-pit mine in which dimension stone, rock, construction aggregate, riprap, sand, gravel, or slate is excavated from the ground. The operation of quarries is regulated in some jurisdictions to reduce their environ ...

along the course of the sill offer sections for its interpretation.

Effects on landscape and geography

The

regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestria ...

supports alpine/Arctic flora which includes spring gentian (''

Gentiana verna ''Gentiana verna'', the spring gentian, is a species of flowering plant in the family Gentianaceae, and one of its smallest members, normally only growing to a height of a few centimetres. The short stem supports up to three opposing pairs of e ...

''), bird's-eye primrose (''

Primula farinosa ''Primula farinosa'', the bird's-eye primrose, is a small perennial plant in the family Primulaceae, native to Northern Europe and northern Asia, and (rarely) farther south at high altitudes in the mountains of southern Europe. This primrose th ...

''), mountain avens (''

Dryas octopetala ''Dryas octopetala'', the mountain avens, eightpetal mountain-avens, white dryas or white dryad, is an Arctic–alpine flowering plant in the family Rosaceae. It is a small prostrate evergreen subshrub forming large colonies. The specific epithet ...

'') and Teesdale violet ('' Viola rupestris''). This is an example of the intimate interaction and dependence of geology and ecology. The resistance to

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

of the dolerite gives rise to a number of striking

geomorphological Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or n ...

features such as

Low Force Low Force is an 18-foot (5.5m) high set of falls on the River Tees, England, UK. Further upstream is the High Force waterfall. Low Force is also the site of the Wynch Bridge, completed in 1830. It is suggested that only one person at a time shou ...

Cauldron Snout Cauldron Snout is a waterfall, cascade on the upper reaches of the River Tees in Northern England, immediately below the dam of the Cow Green Reservoir. It is well upstream of the High Force waterfall, and is on the boundary between County Durham ...

, High Cup Nick and Holwick Scars.

References

{{reflist Geology of Northumberland Paleozoic England Sills (geology)

Derivation of name

Geology

Effects on landscape and geography

See also

References