The island of Fur in the Limfjords consists partly of diatomite and volcanic ash sediments from the Eocene (part of the Paleogene period). The ash was deposited in water. Therefore water animals were suddenly buried in the ash. The ash came from a volcano in the Kattegat in the Eocene period. The ash layers were folded due to the force of the ice in several ice-ages. Fossils from the Moler are quite rare.