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
Ogdens Cave Natural Area Preserve Ogdens Cave Natural Area Preserve Ogdens Cave Natural Area Preserve is a Natural Area Preserve located in Frederick County, Virginia. The preserve protects a cave that carries a below-ground branch of Buffalo Marsh Run, which also flows overland through the preserve. With nearly of the cave mapped, Ogdens Cave is the longest known cave in Frederick County. Several rare invertebrate species are found within the cave, including the thin-neck cave beetle ("Pseudanophthalmus parvicollis"), two amphipods, an isopod, and the Appalachian springsnail ("Fontigens bottimeri"). These species are sustained by nutrients delivered by the cave's stream and by various animals, such as