Wider Significance
Upper Breamish Valley 
Walltown QuarryThe Cheviot volcanic rocks and Cheviot Granite are among the southernmost occurrences of a suite of igneous rocks of late Silurian to Devonian age, the members of which are distributed northwards to Orkney and Shetland. Volcanic rocks of this suite form such notable areas as the Ochil and Sidlaw Hills in the Midland Valley of Scotland, and the caldera-volcano at Glencoe in the Highlands. Though modern studies of the Cheviot rocks are few, these rocks contribute to our wider understanding of this important phase of igneous activity in the evolution of the British Isles.
The Whin Sill is generally regarded as the original sill of geological science and therefore has to be regarded as one of the district’s most important natural heritage features. It takes its name from the north of England quarryman’s term ‘whin’, meaning a black, generally hard and intractable rock, and ‘sill’, meaning any more or less horizontal or flat-lying body of rock. Recognition of an intrusive igneous origin for the Whin Sill during the 19th century was based largely on studies within the present district, notably on sections exposed at Ward’s Hill Quarry. Consequently, the term ‘sill’ became adopted by geological science for all near-horizontal and, within stratified sequences, broadly concordant, intrusive igneous bodies.
Since then, many studies of the Whin Sill-swarm and its associated dykes have drawn upon evidence gathered from its exposures in Northumberland and much of the large volume of earth science literature derived from these studies has significance well beyond the county. In addition to its geological importance, the striking geomorphological expression of the Whin Sill, and its exploitation by the Romans, has produced an internationally recognised landscape.
Geological SSSIs
Carboniferous and Permian Igneous rocks:
- Cottonshope Head Quarry [NT 803 058]
- Steel Rigg to Sewingshields Crags [NY 751 676 to NY 813 704]
- Wydon [NY 695 629]
Geological SNCIs
Allerhope Burn, Barrasford Quarry, Toddle, Reaver, Blindburn, Canker Cleugh, Carshope, Cawfield Crags, Divethill and Claywalls, Earlehill Quarry, Flodden Quarry, Fredden , Preston Yeavering Bell, Haltwhistle Burn, Harelaw etc. Burns, Horsdon Channel, Kyloe Hills, Raker Crag, Shiellow Crags, Shillhope Cleugh, Upper Breamish and Bloodybush Edge, Usway Burn, Walltown Quarry and Crags, Windyhaugh
