It might be entirely natural. It might be the remnant of quarrying. The distinction matters less, perhaps, than the fact that someone thought it worth mapping, then inspecting, and ultimately leaving unresolved.

The hollow appears on the 1933 edition of the Ordnance Survey six-inch map as a hachured feature, meaning it was represented by short radiating lines used by cartographers to indicate a depression or slope in the terrain. When inspectors from the Office of Public Works visited the site in 1982, they could not determine whether the hollow had been dug by human hands or simply formed that way. Because it dates to after AD 1700, it falls outside the period covered by the archaeological record, which generally concerns itself with earlier remains, and so the question was noted and set aside.