The island has an ancient geoformation and, unlike Sicily and mainland Italy, is not earthquake-prone. Its rocks date in fact from the Palaeozoic Era (up to 500 million years old). Due to long erosion processes, the island's highlands, formed of granite, schist, trachyte, basalt (called "jaras" or "gollei"), sandstone and dolomite limestone (called "tonneri" or "heels"), average at between . The highest peak is Punta La Marmora ("Perdas Carpìas" in Sardinian language) (), part of the Gennargentu Ranges in the centre of the island. Other mountain chains are Monte Limbara () in the northeast, the Chain of Marghine and Goceano () running crosswise for towards the north, the Monte Albo (), the Sette Fratelli Range in the southeast, and the Sulcis Mountains and the Monte Linas (). The island's ranges and plateaux are separated by wide alluvial valleys and flatlands, the main ones being the Campidano in the southwest between Oristano and Cagliari and the Nurra in the northwest.