Tom Swift in the City of Gold, Or Marvelous Adventures Underground

According to Wikipedia: "Victor Appleton was a house pseudonym used by the Stratemeyer Syndicate, most famous for being associated with the Tom Swift series of books. The following series have been published under the Victor Appleton name: Tom Swift, 1910–1941; Motion Picture Chums, 1913–1916; Moving Picture Boys, 1913–1922; Movie Boys, 1926–1927; Don Sturdy, 1925-1935; Tom Swift, Jr., 1954–1971 (technically, "Victor Appleton II"); Tom Swift (Third Series), 1981–1984; Tom Swift (Fourth Series), 1991–1993; and Tom Swift (Terror on the Moons of Jupiter). Ghostwriters of these books included Howard Roger Garis, John W. Duffield, W. Bert Foster, Debra Doyle with James D. Macdonald, F. Gwynplaine MacIntyre, Robert E. Vardeman, and Thomas M. Mitchell."