Whin Sill

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The Whin Sill at Crag Lough

The Whin Sill or Great Whin Sill is a tabular layer of the igneous rock dolerite in County Durham and Northumberland in the northeast of England. It lies partly in the North Pennines Area of Outstanding Natural Beauty and partly in Northumberland National Park and stretches from Teesdale northwards towards Berwick.

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 about the same time.[1]

The Little Whin Sill is an associated formation to the south in Weardale.

Derivation of name[edit]

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.









Effects on landscape and geography[edit]

The resultant regolith supports rare alpine/Arctic flora which includes Spring Gentian (Gentiana verna); Bird’s Eye Primrose (Primula farinosa); Mountain Avens (Dryas octupetala) and Teesdale Violet (Viola rupestris). This is an example of the intimate interaction and dependence of geology and ecology.

The resistance to erosion of the dolerite gives rise to a number of striking geomorphological features such as High Force, Low Force, Cauldron Snout, High Cup Nick and Holwick Scars.


  1. ^ D. Liss, W.H. Owens and D.H.W. Hutton, New palaeomagnetic results from the Whin Sill complex: evidence for a multiple intrusion event and revised virtual geomagnetic poles for the late Carboniferous for the British Isles, Journal of the Geological Society; December 2004; v. 161; no. 6; p. 927-938; doi:10.1144/0016-764903-156, 2004 Geological Society of London, England