Old Harry Rocks are three chalk formations, including a stack and a stump, located at Handfast Point, on the Isle of Purbeck in Dorset, southern England.

[citation needed] The downlands of Ballard Down are part of the Portsdown Chalk Formation, containing some bands of flint, and were formed 84–72 million years ago in the Campanian age of the Late Cretaceous.

[1] The bands of stone have been gradually eroded over the centuries, some of the earlier stacks having fallen (Old Harry's original wife fell in 1509), while new ones have been formed by the breaching of narrow isthmuses.

To form the stacks, the sea gradually eroded along the joints and bedding planes where the softer chalk meets harder bedrock of the rock formations to create a cave.

The arch subsequently collapsed to leave the stacks of Old Harry and his wife, No Man's Land (the large outcrop of rock at the end of the cliffs) and the gap of St Lucas' Leap.