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
Spannagel Cave do not support the formation of caves. The only exceptions are pockets of rock capable of karstification such as limestone, dolomite, gypsum and other carbonates. These pockets are generally of quite low thickness, and only allow small caves to be formed. The creation of caves also requires water solubility. The Spannagel Cave has arisen in a large vein of Jurassic calcite marble of the Hochstegen Formation, a marble with over 90% total carbonate content, that runs through the slate mantle of the "Western Tauern window". The formation of this extensive cave as a result of geological corrosion (and mixing corrosion)