The extended range of Monte Rosa, which appears to originate in the intersection of two axes of great elevation, throws out a number of ridges that radiate afar and gradually subside into the plain of northern Italy, covering a relatively large area. There are no convenient mode of subdividing the range. However the natural limits of the district can be defined on the north side by the two branches of the Visp torrent. Following the west branch through the Mattertal, crossing the Theodul Pass, descending by the Valtournanche to Châtillon and to Ivrea, and passing round the base of the mountains by Arona, along Lake Maggiore, and up the valley of the Toce, to Vogogna, then ascending by the Val Anzasca to the Monte Moro Pass, the circuit is completed by the descent through the Saastal to Stalden. Within the line so traced, exceeding 450 km in length, all the ranges properly belonging to this group are included.