Dob's Linn, near Moffat, Scotland, is the location of the Global Boundary Stratotype Section and Point (GSSP) which marks the boundary between the Ordovician and Silurian periods, and marks the base of Llandovery epoch, on the geologic time scale. The area was first studied by Charles Lapworth in the late 19th century, whose work established graptolites as a method of understanding stratigraphic sequences.