Excavated for the Newtown and Machynlleth Railway and opened in 1863, at 211m (693 feet) above sea level this was the highest point on the line and is still in use. When cut sheer through the rock 39m (120 feet) in depth, it was the deepest cutting in the world; the exposure of the geological features led to the discovery of what are now known as 'Talerddig Grits'.
B.A.Malaws, RCAHMW, 1984.