Directed by the dufus of schlock Jerry Warren, the hour-long Incredible Petrified World (1957) is said by some to be his best film, which isn't saying much.

It starts with some stock footage of ocean life that looks like it was shot in a large public aquarium. One cool bit is a fight between a young shark & an octopus, an awfully cruel bit of footage that wouldn't be legal nowadays. The narrator talks about the wonders of the sea. This turns out to be a newsreel shown at a private gathering of sea explorers.

The "best" scenes, by right of being shot in the guano-slimed Colossal Caves in Arizona, are better-looking bits than would otherwise be expected of a no-budget no-imagination affair, plus the cast is better than Warren's talentlessness deserved, leading off with John "Drunk as a skunk" Carradine, Robert "Poor Man's Erroll Flynn" Clarke, & Phyllis "Lois Lane" Coates.

Carradine took such roles only because he was a severe alcoholic, Clarke specialized in Z-grade sci-fi, & Coates had dated the director when they were teenagers in Texas -- which explains his rare good fortune in casting.

The scientist (Carradine) constructs a diving bell in order to look for world food resources in the ultra-deep bottom of the fathomless Carribean. This moronic plan gets his co-stars stuck on the ocean floor near the entrance to the Hollow Earth where there is air, a volcano, a crazy hermit who looks like a cave-man but has merely been stranded for fourteen years, & a passing moment of stock footage of a young water monitor.

The cast wanders or sits in the cavern encountering little of interest, until a second diving bell saves everyone except the crazy hermit just before an underworld volcanic eruption destroys the caverns.