 Similar formations are found at the Giant's Causeway in Northern Ireland, on the island of Ulva and at Ardmeanach on the Isle of Mull. Grooves in the roof of MacKinnon's cave indicate either a pyroclastic flow or a series of eroded ash falls in the rock above the columnar basalt. The 'Staffa Group' is the name given to the series of olivine tholeiite basalts found in the vicinity of Mull which erupted 55 – 58 million years ago.
