Geology
Unusually for the Pennines, rock of volcanic origin, the Whin Sill contributes to the surface geology and scenery of Teesdale. Around 295 million years ago upwelling magma spread through fissures and between strata in the earlier Carboniferous limestone country rock.
Economic deposits in Llandovery rocks include slate pencils.
More recently, Ice Age glacial activity shaped the valley, and much of the pre-glacial river course is now buried beneath glacial drift.
Read more about this topic: Teesdale