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
Cave-in-Rock State Park the meltoff following the Wisconsin ice age. It was not formed by typical karst processes like Mammoth Cave in nearby Kentucky; it is a tunnel eroded into the bluff. Cave-in-Rock was known and used for thousands of years by the Native Americans. The first European to discover the Cave was M. de Lery of France, who in 1729 mapped and named it ""caverne dans Le Roc"" (cf. supra). This name, translated directly into English, is the name the cave bears to this day. Other names for the cave included Rock-In-Cave, Rocking Cave, Rock-and-Cave, House of Nature, The Cave, Big Cave,