Igneous rock the partial melting of rocks within the mantle and crust. Extrusive igneous rocks cool and solidify quicker than intrusive igneous rocks. They are formed by the cooling of molten magma on the earth's surface. The magma, which is brought to the surface through fissures or volcanic eruptions, solidifies at a faster rate. Hence such rocks are smooth, crystalline and fine-grained. Basalt is a common extrusive igneous rock and forms lava flows, lava sheets and lava plateaus. Some kinds of basalt solidify to form long polygonal columns. The Giant's Causeway in Antrim, Northern Ireland is an example. The molten rock, with
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