East Texas outcrops consist of Cretaceous and Paleogene sediments which contain important deposits of Eocene lignite. The Mississippian and Pennsylvanian sediments in the north; Permian sediments in the west; and Cretaceous sediments in the east, along the Gulf coast and out on the Texas continental shelf contain oil. Oligocene volcanic rocks are found in far west Texas in the Big Bend area. A blanket of Miocene sediments known as the Ogallala formation in the western high plains region is an important aquifer. Located far from an active plate tectonic boundary, Texas has no volcanoes and few earthquakes.