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
S bridge part of the original National Road, which was built circa 1825. The S Bridge in Berks County, Pennsylvania, and the Claysville S Bridge in Washington County, Pennsylvania, are listed on the National Register of Historic Places. Another S bridge, in Anderson County, Kentucky, is located on U.S. Route 62 east of Lawrenceburg. It has undergone major roadway replacement and has been widened. Another S bridge of note is located in Hertford, North Carolina. It connects a causeway from Winfall to the Town of Hertford, over the Perquimans River. S bridge An S bridge is a bridge whose alignment follows a