The Whin Sill appears and then disappears

The Whin Sill is a 294 million year old dolerite (basaltic rock) intrusion that appears at various points in the counties of Durham and North Yorkshire. When it does appear above the surface, the results are spectacular.

When building Hadrian’s Wall, from Solway Firth in the West, to Wallsend on the east coast of England, the Whin Sill came in very useful. The crags to the north and east of the village of Haltwhistle in Northumberland provide a massive natural wall against would be invaders from the north.

At High Cup Nick overlooking the Eden valley and Cumberland, now Cumbria, the Whin Sill forms a huge row of cliffs frowning above the enormous U-shaped valley scoured out by glaciers in the Ice Age.

At High Force on the River Tees, water tumbles over the Whin Sill, forming England’s largest waterfall. Higher up the Tees valley, near Cow Green Reservoir, which has taken a lot of the spate out of the beck (stream), Cauldron Snout provides yet another appearance of the granite intrusion.

And downstream from High Force, the aptly named Low Force shows its teeth as the Whin Sill surfaces briefly again.

Happily, Pennine Way walkers meet up with the sill again and again as they step towards the border of England and Scotland.
Robert L. Fielding