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-In-Rock, Illinois 43.8% of those under age 18 and 24.1% of those age 65 or over. Cave-in-Rock's primary feature is a striking riverside cave formed by wind and water erosion and by cataclysmic effects of the 1811–12 New Madrid earthquakes. The cave is located at , just upriver (east) from the village. The first European to come across it was M. de Lery of France, who found it in 1739 and called it ""caverne dans Le Roc"". Other names for the cave include Rock-In-Cave, Rocking Cave, Rock-and-Cave, House of Nature, The Cave, Big Cave, and Murrell's Cave. The cave is the main