At the Earths Core, by Edgar Rice Burroughs.
When David Innes and his inventor friend Abner Perry pierced the Earths crust in their Iron Mole, never did they expect to find a fantastic inner world of eternal daylight! A world where prehistoric monsters still live and battle with cave men and women against and even more inhuman master!
The Land that Time Forgot by Edgar Rice Burroughs.
In 1916 the US Montrose is fired on and sunken by a German U-boat. However the survivors manage to sneak aboard and capture the U-boat. In between subsequent coups, the British and Germans agree to an uneasy truce until they can reach a neutral port. But they become lost and instead arrive on the mythical continent of Caprona where dinosaurs and cavemen still roam.
