At the Earth's Core, BACK TO THE STONE AGE, Edgar Rice Burroughs, (Pellucidar Series #5)

In the previous Pellucdar (TARZAN AT THE EARTH’S CORE) the crew left LT. Von Horst behind because they thought he was dead. He wasn’t. Now he has to battle his way to freedom in a hostile land filled with dinosaurs and savages. But love can be found in the strangest places.