Written in Stone: geology and graffiti in Orkney

Orkney’s story has always been written in stone. Underneath its rich soil
lie thick layers of Devonian flagstone, laid down as sediments when the
islands were submerged under Lake Orcadie millions of years ago. The
ghosts of old sun-cracks and wave ripples are often visible in the strata,
along with the fossilized remains of ancient fish: the ichthyolites of the
famous Sandwick Fish Bed. These lake deposits helped form the rolling
landscape of Orkney today; soft hills giving way to sea-cliffs, indented by
deep geos along lithic flaws in the readily-fractured flagstone. Its
properties have been exploited from the earliest times, quarried for walling
stone and roof-slates from the Neolithic to the present day.