Frank and Andy Afloat or The Cave on the Island

Popular children's book, first published in 1921. Published under fictitious name. According to Wikipedia: "This list of Stratemeyer Syndicate series gives the titles of all series produced by the book-packaging firm the Stratemeyer Syndicate. The Syndicate was founded by Edward Stratemeyer and is best known for producing the Bobbsey Twins, Hardy Boys, Nancy Drew, Rover Boys, and Tom Swift series. The Syndicate produced these and many other series in assembly-line fashion: one person wrote the outline for a story or series of stories, another wrote the story itself, and often still another edited the work. Most Syndicate books were published under pseudonyms. The authors named in this list are those credited as having written the series; in most cases, the names are fictitious."