Note: Translated and "adapted" by Farmer from the French. According to the Encyclopedia of Science Fiction (3rd edition), the original French text was "so drastically modified that it cannot be regarded as the same work."

Synopsis: Somewhere in the unexplored heart of Africa a part of this Earth had been taken over by an intelligence from outer space. Such was the message that reached the explorer Hareton Ironcastle, member of the famous Baltimore Gun Club. In that hidden and transformed valley would now be found monsters and pre-humans not to be seen anywhere else. Such a challenge could not be ignored, and the account of Ironcastle's expedition of daring but inexperienced amateurs became one of the classic novels of the French writer J. J. Rosny, who was a contemporary of Verne, Wells, and Edgar Rice Burroughs. Now Philip Jose Farmer, Hugo winner and chronicler of the adventures of Tarzan and Doc Savage, has translated and retold Rosny's novel, making it a marvel adventure novel to stand alongside the works of Burroughs, Haggard and Farmer himself. (from the back cover of the DAW Books first edition)