A Journey to the Earth’s Interior or Have the Poles Really Been Discovered – Gardner, Marshall B. (PDF)

The Book of Earths – Kenton, Edna (PDF)

The Smoky God, or, a Voyage to the Inner World – Emerson, Willis George (PDF)

Etidorpha or The End of Earth, The Strange History of a Mysterious Being and The Account of a Remarkable Journey – Lloyd, John Uri (PDF)

The Hollow Earth, The Greatest Geographical Discovery in History Made by Admiral Richard E. Byrd in the Mysterious Land Beyond the Poles, The True Origin of the Flying Saucers – Bernard, Raymond W. (PDF)