The Carboniferous is the second youngest period of the Paleozoic Era, 363 to 286 million years ago. In this period the coastal plains in North-western Europe were covered with primeval tropical forests. They were regularly flooded and covered with marine sediments. Residues of the trees that used to grow there consequently survived and eventually carbonised. Museon’s collection includes many plant fossils in the shape of leaf imprints, petrified stems and root stocks.