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
Geological history of the Precordillera terrane range)—literally "pre-mountain range"—and applied usually to the Andes. The Precordillera is in western Argentina and can be traced by the thrust-fold belt. It is about 200 km wide, and stretches 800 km from latitude 29°S to 33°S in western Argentina, with its south end in Mendoza, through San Juan, to La Rioja in the north. The northern and southern boundaries are not precisely defined. In terms of geological regions, the northeastern boundary connects to the western Pampeanas and the Famatina ranges, and the eastern margin connects to the frontal cordillera then the Chilenia Terrace. The Early-Cambrian to Ordovician deposits of