High Cup Nick, near Dufton in Cumbria, lies at the head of High Cup Gill, a broad u-shaped valley topped with formidable crags. These rocks are part of series known as the Great Whin Sill, which range from the Northumberland coast across northeast England, through the Pennines and just into Cumbria. Formed from dolerite magma squeezing itself into gaps in the surrounding rocks, which has created tabular layers a little like the jam in a sandwich. Here they were intruded into carboniferous limestone, which, being softer, has since been eroded away by glaciers and rivers. Now a narrow beck runs over the rocks, except when frozen, and meanders away across a marshy valley floor.