Whin Sill
The Whin Sill or Great Whin Sill is a tabular layer of the
It is one of the key natural features of the North Pennines. A major outcrop is at the High Force waterfall in Teesdale. Bamburgh Castle, Dunstanburgh Castle, Lindisfarne Castle and stretches of Hadrian's Wall 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, Alnwick Sill and the Hadrian's Wall-Pennines Sill, which were created by separate magma flows, but at about the same time.[1]
The Little Whin Sill is an associated formation to the south, in Weardale.
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.[2]
Geology
Towards the close of
It underlies much of south and east Northumberland and the Durham Coalfield. 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 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-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
The
Disused roadstone quarries along the course of the sill offer sections for its interpretation.
Effects on landscape and geography
The regolith supports alpine/Arctic flora which includes spring gentian (Gentiana verna), bird's-eye primrose (Primula farinosa), mountain avens (Dryas octopetala) and Teesdale violet (Viola rupestris). This is an example of the intimate interaction and dependence of geology and ecology.
The resistance to
See also
References
- , 2004 Geological Society of London, England
- ^ Hudspeth, Sarah. "Whin Sill". North Pennines AONB. Retrieved 8 July 2020.
- ^ "Variscan Orogeny". Geological Society. Retrieved 18 February 2020.
- ^ "GeoIndex Onshore". British Geological Survey. Retrieved 8 July 2020.