Sep 28, 2015
"Giant's Causeway" / "Clochán an Aifir" (40,000 interlocking columnar basalt structures) Antrim, Ireland: the pillarlike remains of a Paleogene volcanic eruption. Molten basalt penetrated the surface from underneath a field of chalk, where lava then began cooling and solidifying into the geometric rock-formations seen at present. © NERC London/Cooper/Institute of Geological Sciences. photo by Ed Cooper