Like the rock on which Edinburgh Castle is built, it was formed by an extinct volcano system of Carboniferous age (lava samples have been dated at 341 to 335 million years old), which was eroded by a glacier moving from west to east during the Quaternary (approximately the last two million years), exposing rocky crags to the west and leaving a tail of material swept to the east. This is how the Salisbury Crags formed and became basalt cliffs between Arthur 's Seat and the city centre. From some angles, Arthur 's Seat resembles a lion couchant. Two of the several extinct vents make up the ' Lion 's Head ' and the ' Lion 's Haunch '.
when was the last time arthur's seat erupted
lava samples have been dated at 341 to 335 million years old