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
Prometheus Cave Natural Monument makes Prometheus enchained to the bluffs of Khvamli, being perpetually tortured by a raven.) In a year cave was refurnished and reopened to visitors on May 26, 2011. Prometheus Cave Natural Monument Prometheus Cave Natural Monument () also known as "Kumistavi Cave" () and "Tsqaltubo Cave" () is a karst cave located in Tsqaltubo Municipality in Imereti region of Georgia. The total length of the cave is about 11 km, of which 1060 m are open to visitors. Cave has total of 22 halls of which six are currently open to tourists. The cave was discovered and studied by Georgian