Geography: The Most Famous Natural Landmark In __________________ Is The Giant's Causeway. Comprised Of Approximately 37,000 Dark Basalt Columns Packed Together, They Were Formed When A Volcanic Eruption Spewed Molten Basalt Out 55 Million Years Ago. As The Basalt Cooled, These Unique Polygonal Structures Were Formed. Most Of The Columns Of The Giant's Causeway Form A Six-Sided Honeycomb Pattern. Some Have As Many As Ten Sides And Measure About 12 Inches Across And Up To Forty Feet In Length