The Matterhorn is mainly composed of gneisses (originally fragments of the African Plate before the Alpine orogeny) from the Dent Blanche nappe, lying over ophiolites and sedimentary rocks of the Penninic nappes. The mountain's current shape is the result of cirque erosion due to multiple glaciers diverging from the peak, such as the Matterhorn Glacier at the base of the north face. Sometimes referred to as the Mountain of Mountains (), the Matterhorn has become an iconic emblem of the Alps in general. Since the end of the 19th century, when railways were built in the area, the mountain has attracted increasing numbers of visitors and climbers. Each year, numerous mountaineers try to climb the Matterhorn from the Hörnli Hut via the northeast Hörnli ridge, the most popular route to the summit. Many trekkers also undertake the 10-day-long circuit around the mountain. The Matterhorn has been part of the Swiss Federal Inventory of Natural Monuments since 1983.