The rocks of Monte Generoso are constituted of flinty limestone, a sedimentary rock that originated from the depths of the sea, 200 million years ago. It is formed by the shells of molluscs and the skeletons of dead marine vertebrates. The deposits here reached a considerable thickness. Not all the animals were turned into fossils. The majority rotted without leaving any trace.
The formation of a fossil, therefore, is a major event that takes place only when the animal is quickly buried and removed from any contact with the air.
Thus, the fossils are documents that reveal the story of Monte Generoso.