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
Crag Cave Crag Cave Crag Cave is a cave in Ireland, located just outside Castleisland, County Kerry. Formed in elevated limestone rock, the system extends to of surveyed passage, on two levels. It is the 7th-longest cave system in the Republic of Ireland, and the 10th-longest in the whole of Ireland. While the Geological Survey of Ireland in 1859 acknowledged the presence of "caves worn by water, some of which can be traversed for some distance," positive efforts at exploration were not made until 1981, when the upper part of the cave was explored to a sump, named the "Green Lake". When