Also known as In Caverns Below.
A cliff overlooking tremendous galleries and caverns and far below, two armies battling with powerful destructive weapons... this was the place into which Comstock and Clay had been thrust by what they thought was an earthquake. Here, below the desert — below the silver mine which the two had been exploring — were two hidden civilizations, deadly enemies, and the possessors of far-advanced scientific secrets.
Separated from his companion, Frank Comstock found himself captured by chalk-faced people and brought into a civilization that was both bewildering and awe-inspiring. For while the people of this Alice-in-Wonderland of Wu appeared to be scientific geniuses, they looked and acted like madmen!
Stanton Arthur Coblentz (1896–1982) was an American author and poet. He received a Master's Degree in English literature and then began publishing poetry during the early 1920s. His first published science fiction was "The Sunken World," a satire about Atlantis, in Amazing Stories Quarterly for July, 1928. The next year, he published his first novel, The Wonder Stick. But poetry and history were his greatest strengths. Coblentz tended to write satirically. He also wrote books of literary criticism and nonfiction concerning historical subjects. Adventures of a Freelancer: The Literary Exploits and Autobiography of Stanton A. Coblentz was published the year after his death.
Stanton A. Coblentz. Wikipedia.