Is the volcanic upland plain of the Giara (1998 ft.) and south of the Sarcidano are the districts known as the Trexenta, with lower, fertile hills, and the Sarrabus, which culminates in the Punta Serpeddi (3507 ft.), and the Monte dei Sette Fratelli (3333 ft.), from the latter of which a ridge descends to the Capo Carbonara, at the S.E.
Its importance is due to its command of the point where the chief trade route from Persia and Central Asia to Europe, over the table-land of Armenia by Bayezid and Erzerum, descends to the sea.
The principal affluents are the AriCge, the Tarn with the Aveyron and the Agout, the Lot and the Dordogne, which descends from Mont Dore-lesBains, and joins the Garonne at Bec-dAmbez, to form the Gironde.
All these affluents are on the right, and with the exception of the Arige, which descends from the eastern Pyrcnees, rise in the mountaitis of Auvergne and the southern Cvennes, their sources often lying close to those of the rivers of the Loire and Rhone basins.
Is watered by the secondary system of the Charente, which descends from ChCronnac (Haute-Vienne), traverses Angoulme and falls into the Atlantic near Rochefort.