Castle Rock

Castle Rock is a volcanic plug in the middle of Edinburgh upon which Edinburgh Castle sits. The rock is estimated to have formed some 350 million years ago during the early Carboniferous period. It is the remains of a volcanic pipe which cut through the surrounding sedimentary rock, before cooling to form very hard dolerite, a coarser-grained equivalent of basalt. Subsequent glacial erosion was resisted more by the dolerite, which protected the softer rock to the east, leaving a crag and tail formation.

The summit of the castle rock is 130 m above sea level, with rocky cliffs to the south, west and north, rearing up to 80 m from the surrounding landscape. This means that the only readily accessible route to the castle lies to the east, where the ridge slopes more gently.