In 1858, Snider-Pellegrini published his book, La Création et ses mystères dévoilés ("The Creation and its Mysteries Unveiled"). He proposed that all of the continents were once connected together during the Pennsylvanian Period. He based this theory on the fact that he had found plant fossils in both Europe and the United States that were identical. He found matching fossils on all of the continents. He also attributed the cause of the fragmentation of the supercontinent to the Great Flood of the Bible.