The Land that Time Forgot

For an instant I was fearful for myself, and then I saw that which filled me with a far greater terror for another.
Book #18 of 20 in the SDE Classics Science Fiction Collection
After capturing a German U-Boat in World War I, an American, his British comrades, and their German prisoners set out in the Atlantic Ocean only to find a mystical Island named Caspak. In desperate search for a way home, they come across early man in every stage of development, a saber-toothed tiger, and even dinosaurs.