thumb|right|Old Harry and his (latest) wife
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. They mark the most eastern point of the Jurassic Coast, a UNESCO World Heritage Site.
Location
Old Harry Rocks lie directly east of Studland, about north east of Swanage, and about south of the large towns of Poole and Bournemouth. To the south are the chalk cliffs of Ballard Down, the Pinnacle and Little Pinnacle, much of which is owned by the National Trust. The rocks can be viewed from the Dorset section of the South West Coast Path.
Formation
The chalk of Old Harry Rocks used to be part of a long stretch of chalk between Purbeck and the Isle of Wight, but remained as a headland after large parts of this seam were eroded away. As the headland suffered hydraulic action (a process in which air and water are forced into small cracks by the force of the sea, resulting in enlarging cracks), first caves, then arches formed. The tops of the arches collapsed after being weakened by rainfall and wind, leaving disconnected stacks. One of these stacks is known as Old Harry. Old Harry's Wife was another stack which was eroded through corrosion and abrasion, until the bottom was so weak the top fell away, leaving a stump. Hydraulic action is the main cause of erosion (shear force of the waves) that damaged the rock and caused it to fall away.
Geology
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. 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.
Legend
There are various stories about the naming of the rocks. One legend says that the Devil (traditionally known euphemistically as "Old Harry") slept on the rocks. Another local legend says that the rocks were named after Harry Paye, the infamous Poole pirate, whose ship hid behind the rocks awaiting passing merchantmen.
Yet another tale has it that a ninth-century Viking raid was thwarted by a storm and that one of the drowned, Earl Harold, was turned into a pillar of chalk.
In popular culture
The ashes of novelist H G Wells were scattered in the water off Old Harry Rocks.