A small steep valley north of the road between Moffat and Selkirk in Dumfries and Galloway, inside the National Trust for Scotland’s Grey Mare’s Tail reserve, and one of the reference points of the geological timescale. The International Union of Geological Sciences ratified it in 1984 as the Global Boundary Stratotype Section and Point for the base of the Silurian: the boundary is drawn at the first appearance of the graptolites Parakidograptus acuminatus and Akidograptus ascensus, 1.6 metres above the base of the Birkhill Shale. Charles Lapworth worked out the sequence here in the late 19th century and effectively invented graptolite biostratigraphy doing it. The place is named for Halbert Dobson, a covenanter who hid in the linn from government troops during the Killing Time.
Graptolites at the Ordovician and Silurian golden spike · Ordovician to Silurian boundary, ~443 mya
This ground is protected. Photograph it, record it, leave it where it lies. On US federal land the Paleontological Resources Preservation Act 2009 makes collecting vertebrate fossils an offence, and penalties are real.
United Kingdom
See it on the map
Other places on the map within a couple of hours.
