The Great Stone of Sardis

A double adventure written at the end of the 19th century, somewhat in the theme of Jules Verne's Twenty Thousand Leagues Under the Sea and Journey to the Center of the Earth, telling of a submarine trip in the year 1947 to reach the North Pole and a project to examine the center of the Earth by boring a deep shaft. What they find at the core of the planet surprises the enterprising explorers.