... being the north facing scarp in Northumberland upon which part of Hadrian's Wall stands. The Farne Islands are part of the sill, as are the crags at Bamburgh, which are home to the castle. The coastline between Dunstanburgh and Cullernose Point, as well as the rock that leads to High Force waterfall in Co. Durham are also parts of the Whin Sill. The Whin Sill has a total area of at least 5000 square kilometres.(Eastwood, 1971) As the sill is made up of a number of lenses, the number varying with location (5 lenses were found in certain parts of Northumberland), the thickness varies accordingly, although the common thickness is about 100ft. The greatest depth discovered was at the Burtree Pasture Lead Mine in Weardale, which had a thickness of 240ft. The sill itself is made up of a variety of rock types, the most abundant being a dark coloured, blue-grey ...

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