Rocks that have solidified from a molten state deep in the earth. Those rocks that hive reached the surface while still molten are called lavas; they can form volcanic cones or spread out in flows or sheets, they can be forcibly thrust up between beds of other kinds of rocks in what are called sills, or they can fill crevices and then solidify as "dikes." Rocks that have solidified deep beneath the earth's crust are referred to as plutonic, from the greek god of the lower regions, pluto. Granite is an example of plutonic rock.
