As a St. Patrick’s Day treat, here’s a great photo of one of Ireland’s most famous geologic locales, Giant’s Causeway.  Formed from a Paleogene (40-50 mya) basaltic lava flow, rapid cooling and contraction resulted in some 40,000 columns and one very picturesque coastline.  Photo credit goes to All That is Interesting.

Giant's Causeway, Northern Ireland