The Land That Time Forgot is the first of Edgar Rice Burroughs's Caspak trilogy. It begins with terror on the high seas: a German submarine torpedoes an American liner in the English Channel. Our hero, young Bowen J. Tyler, Jr., clings to life in a single surviving lifeboat. He rescues his dog, Nobs, and a beautiful young woman named Lys La Rue--whom he instantly falls in love with.
The three are picked up by an English tug, which has the misfortune to run into the same German submarine which sunk the American liner. This time, the Allies get the upper hand. They trick the Germans and storm the submarine, taking control of U-33.
Tyler and the rest try to sail the submarine into an English port, but sabotage by the German prisoners (or somebody) gets them lost. They stumble upon the lost island of Caprona in the Antarctic Sea. Caprona--or Caspak, as the natives call it--is a huge island rearing hundreds of feet out of the sea. The sides are sheer impassable cliffs. Over the cliffs, on Caspak, lies an ancient primitive land from Earth's forgotten past. Volcanic heat creates a tropical atmosphere that supports lush forests. Dinosaurs and savage, pre-historic beasts roam the land. Ape men eke out a meagre existence. Out of oil for the submarine's engines and out of food and water for the men, Tyler and his crew must survive on Caspak.
Most don't survive, of course. And the German prisoners are up to no good. This book was written during the first World War, and it shows.
It's a good book, marred by a few throwaway lines of subtle racism.
The Land That Time Forgot is out of copyright. It is freely and legally available online at Project Gutenberg: The Land That Time Forgot.