Editing Old Harry Rocks (section)

== Geology ==
The [[downland]]s 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]].<ref name=ianwest>{{cite web |url=https://wessexcoastgeology.soton.ac.uk/Harry-Rocks.htm |title=Geology of Harry Rock sand Ballard Point |access-date=2007-12-21 |work=Geology of the Wessex Coast of Southern England }}</ref> The bands of stone have been gradually [[erosion|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.<ref name=ianwest/> 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 (the large outcrop of rock at the end of the cliffs) and the gap of St Lucas' Leap.

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".<ref>Shifting Shores. Living with a changing coastline (National Trust)</ref>