This is one of Kuttner's 1947 pulp magazine stories that may have been expanded for the paperback. Like much of his work it's possibly co-authored by his wife C. L. Moore. Many of their early collaborations were published under the names Lawrence O'Donnell or Lewis Padgett. As she later said, getting the rent paid was often more important then arguing over the direction of the story.

This is the least impressive of his books. As one of the pioneers of classic SF all his/their works deserve a read. They are still respected as great innovators of the genre. I'll keep reading his/their stories. ( )

I enjoyed the surreal, at times almost Lovecraftian sensibility of this one, but its hokeyness quotient is also quite elevated. While the "encounter with a lost civilization hidden in the remote Amazon" concept is hardly an original premise for a story of this ilk, Valley of the Flame does offer some intriguing twists, most notably a "bubble" zone in which each living being's metabolism and time-sense flows much more quickly than in the outside world, which has allowed an evolutionary process to run its full course while little time has past in the outside world. Having said that, at its heart this is really a rather conventional pulp story in which the hero explores a fantastic setting, fights a villain, saves the day, and gets the "girl". ( )