Thomas also suggested that the Altar Stone was probably taken from old red sandstone rocks found to the south and east of the Mynydd Preseli, on the presumed bluestone transport route to Stonehenge.

The 449ft (137m) sea stack is formed of old red sandstone and stands close to Rackwick Bay on the west coast of the island of Hoy. It is one of the UK's tallest sea stacks and can be seen from the ...