Jacques Vallee, The Invisible College:

In “The Invisible College” Vallee describes a San Francisco new age gathering where a man who calls himself Allen the Messiah is advertising “the everlasting gospel reveled to him by the saucers.”

“His information indicates that the Earth is, in fact, hollow with the Saucer People inside. “Do you really believe that?” Asks a friend of mine. “Certainly” he replies. “If you were going to make a planet, would you waste all that good dirt?”