Edgar Rice Burroughs is best known for two creations: John Carter of Mars and Tarzan of the Apes. A lesser known series is the Caspak Trilogy contained in this work, but in many respects it is his most creative and provocative of all of his formula fiction. Imagine a land where all creation and evolution is taking place simultaneously, and you have the germ of a great story. Burroughs does not use this theme well, falling into his repetitive formula of placing his characters in constant peril at the end of each chapter, but that was a staple of pulp magazine writing in the early 1900s, and it certainly paid off for him, so I give him the benefit of the doubt. The sheer magnificense of the concept alone makes this a valuable work despite the formula writing, especially for Burroughs fans.