Stratotype for the Ordovician-Silurian boundary. Figured out by Charles Lapworth, using graptolites.
Found cropping out along the beach at Barns Ness, east of Dunbar, Scotland.
Chalk, chert, and basalt predominate.
Spot the basking grey seals.
Hutton's classic unconformity (Devonian red beds over Silurian graywacke and shale).
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