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 State Park the meltoff following the Wisconsin ice age. It was not formed by typical karst processes like Mammoth Cave in nearby Kentucky; it is a tunnel eroded into the bluff. Cave-in-Rock was known and used for thousands of years by the Native Americans. The first European to discover the Cave was M. de Lery of France, who in 1729 mapped and named it ""caverne dans Le Roc"" (cf. supra). This name, translated directly into English, is the name the cave bears to this day. Other names for the cave included Rock-In-Cave, Rocking Cave, Rock-and-Cave, House of Nature, The Cave, Big Cave,