The locality known as Dob's Linn lies XX km NE of the town of Moffat in the Southern Uplands of Scotland, about half way between Glasgow and Carlisle. The name Dob's Linn originates from the name of a 17th C covenanter, Halbert Dobson, who escaped from Government soldiers by hiding under the waterfall in the Linn Branch. The rocks which crop out at Dob's Linn have been studied for over 100 years because they yield abundant fossil graptolites. The rocks comprise sequences of grey mudstones and black shales which form the Moffat Shale Group and span the Upper Ordovician and Lower Silurian.
Graptolite fossils are commonest in the black shales.
The importance of Dob's Linn as a classic geological locality was established in 1878 by Charles Lapworth , an amateur geologist, while he was a school teacher at St Andrews. He recognised that evolutionary changes in graptolite genera and species could be used to discriminate between different stratigraphical horizons. He also established the Ordovician system. The scheme he devised for Dob's Linn was applied to other horizons of similar age and shown to be valid. Since then graptolites have become one of the most important zone fossils for correlating Ordovician and Silurian successions world-wide.