Climacograptus wilsoni graptolite fossils on black shale (26 x 25 millimetres) of middle Ordovician age (Soudleyan Stage, ~mid-Caradocian) from the main cliff at Dob’s Linn (about 36.1-43.1 metres below the Ordovician-Silurian boundary GSSP
The boundary is defined as the first appearance of graptolitesParakidograptus acuminatus and Akidograptus ascensu 1.6 m above the base of the Birkhill Shale Formation. The shale section also contains chitinozoa and conodonts, but neither are well preserved. Dob's Linn has been criticized for the difficulty in relating its graptolite biostratigraphic sequence with shallow water sequences elsewhere, although the stratotype also appears to correspond with a carbon-13 isotope excursion in the latest Ordovician which can be identified worldwide.
^Underwood, C J; S F Crowley; J D Marshall; P J Brenchley (July 1997). "High-resolution carbon isotope stratigraphy of the basal Silurian Stratotype (Dob's Linn, Scotland) and its global correlation". Journal of the Geological Society. 154 (4): 709. doi:10.1144/gsjgs.154.4.0709.