One of the most notable occurences of whinstone in the British Isles is the Great Whin Sill, which runs through Northumberland, just south of Scotland. At places it is over 200 feet thick, and where it protrudes above the surface it can be quite a formidable structure. Part of Hadrian’s Wall runs atop the Great Whin Sill.

Arguing that the Sill was a volcanic intrusion would have been difficult to do in 1817, since it would have required explaining where so much molten rock had come from, and Winch does not go that far in his paper on the geology of Northumberland. But his map does provide the location of the Sill, which appears as a long green stripe.

For the exhibition we display the entire map. For the catalog, we reproduce a detail. If you look closely (see the larger view), you can also see the track of Hadrian’s Wall on top of the Sill.