Metamorphic rocks are sedimentary or igneous rocks whose physical and mineralogical characteristics have been profoundly altered by the action of heat or pressure, or both. The principal metamorphic rocks are schist, phyllite, gneiss, marble, quartzite, and slate. Some metamorphic rocks can also be found in glacial deposits in northern Kentucky. Metamorphic rocks also exist in the deep subsurface of Kentucky and have been encountered in oil and mineral drill holes. The nearest surface exposures of metamorphics are in the Blue Ridge and Piedmont areas of Virginia, West Virginia, and the Carolinas, and the Great Smoky Mountains in Tennessee and North Carolina.