Input (grade 13): It is formed entirely from hexagonally jointed basalt columns, similar in structure to (and part of the same ancient lava flow as) the Giant's Causeway in Northern Ireland and those of nearby Ulva.
Output (grade 8): It is formed entirely from hexagonally jointed basalt columns. These are part of the same ancient lava flow as the Giant's Causeway in Northern Ireland and those of nearby Ulva.