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, 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 that damaged the rock and caused it to fall away.
Geology
The downlands of Ballard Down are formed of chalk with some bands of flint, and were formed approximately 66 million years ago. The bands of stone have been gradually eroded over the centuries, some of the earlier stacks having fallen, while new ones have been formed by the breaching of narrow isthmuses. Across the water to the east The Needles on the Isle of Wight are usually visible. These are also part of the same chalk band and only a few thousand years ago were connected to Ballard Down. 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. This eventually eroded right through to create an arch. The arch subsequently collapsed to leave the stacks of Old Harry and his wife, No Man's Land and the gap of St Lucas' Leap. The large outcrop of rock at the end of the cliffs is often referred to as "No Man's Land". Old Harry is formed by erosion processes, which will eventually remove the stack, whilst new stacks develop. Some people desire to preserve the rocks and protect them from the erosive processes that formed Old Harry. The National Trust, who own the stacks in perpetuity, have experience in looking after the coast, and have found that "working with natural processes is the most sustainable approach".
Legend
There are various stories about the naming of the rocks. One legend says that the Devil 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.
