Giant's Causeway cases the horizontal fracture has resulted in a bottom face that is convex while the upper face of the lower segment is concave, producing what are called "ball and socket" joints. The size of the columns is primarily determined by the speed at which lava from a volcanic eruption cools. The extensive fracture network produced the distinctive columns seen today. The basalts were originally part of a great volcanic plateau called the Thulean Plateau which formed during the Paleocene. According to legend, the columns are the remains of a causeway built by a giant. The story goes that the Irish
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