Top Secret: 1984's Stonehenge Free Festival hollow stem cutter head
augered 1) concrete, 2) brass, 3) wood; and 4) ferromagnetic iron.
Horseshoe magnet lowered in hollow stem auger hole confirmed
ferromagnetic iron below the Heel Stone calf head, 1.2m (4ft)
below Stone base, with iron traces lodged in cutter head.