Geology of Ireland longest known free-hanging stalactites. Geology of Ireland The geology of Ireland consists of the study of the rock formations in Ireland. The island contains rocks from every age from Proterozoic to Holocene and a large variety of different rock types is represented. The basalt columns of the Giant's Causeway together with geologically significant sections of the adjacent coast have been declared a World Heritage Site. The geological detail follows the major events in Ireland's past based on the geological timescale. The oldest known Irish rock is about 1.7 billion years old and is found on Inishtrahull Island off the north
Fingal's Cave the name as Fingal (meaning "white stranger") through a misapprehension of the name which in old Gaelic would appear as Finn. The legend of the Giant's Causeway has Fionn or Finn building the causeway between Ireland and Scotland. The cave has a large arched entrance and is filled by the sea. Several sightseeing cruises organised from April to September by local companies pass the entrance to the cave. In calm conditions, one can land at the island's landing place (as some of these cruises permit) and walk the short distance to the cave, where a row of fractured columns forms