This series consists of seven novels, written by Burroughs and published between 1913 and 1963. Titles include: At the Earth's Core, Pellucidar, Tanar of Pellucidar, Tarzan at the Earth's Core, Back to the Stone Age, Land of Terror and Savage Pellucidar. In 1976, Ace issued a paperback sequel entitled Mahars of Pellucidar by John Eric Holmes.