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 of La Pasiega — mainly owing to the difficult historical circumstances of Spain in the 1930s. After this, in 1952, while a eucalyptus plantation was being put in, another cave was found with a small monetary treasure of the 17th century: hence the new cave was called "Las Monedas": in it, however, was found a rock sanctuary with important pictures and drawings. In light of this, the engineer Alfredo García Lorenzo concluded that Monte Castillo held more secrets. Therefore, a geological survey was set in motion which resulted the following year in the discovery of another cave with rock paintings, "Las Chimeneas" ("The