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
Geological Society of Washington Geological Society of Washington The Geological Society of Washington is a learned society based in the Washington, D.C. area. According to its constitution, "The object of the Society is the increase and diffusion of geological knowledge" The Geological Society of Washington (GSW) was founded in 1893. The core group of organizers was paleontologist C. D. Walcott and geologists S. F. Emmons and J. S. Diller of the United States Geological Survey (USGS), and artist/geologist W. H. Holmes and geologist G. P. Merrill of the Smithsonian Institution. By the end of February, 1893, they had drafted a constitution and attracted a