Other important testimonies are the fossiliferous deposits, such as the so-called Tyrrhenian bench, rich in Quaternary fossils, present in the Tavolara slope facing Libeccio. Finally, the fossil beaches, or beach rock, are important indicators of ancient sea levels. These formations composed of square blocks of sandstone and conglomerates, consolidated by the precipitation of carbonates, are regularly cracked and have an elongated shape. They represent the sandy cordons that delimited large stretches of coastline. Thanks to these numerous testimonies it has been possible to trace the change in the shape of the island of Tavolara over time, discovering that it became an island only 8000 years ago. At that time it was probably still connected to the Isola Piana, by a tombolo structure, like the sandy cordon that still joins the last strip of the Spalmatore di Terra to Tavolara (the Passetto).