Turkey's terrain is structurally complex. A central massif composed of uplifted blocks and downfolded troughs, covered by recent deposits and giving the appearance of a plateau with rough terrain, is wedged between two folded mountain ranges that converge in the east. True lowland is confined to the plain of the Ergene river in Thrace, extending along rivers that discharge into the Aegean Sea or the Sea of Marmara, and to a few narrow coastal strips along the Black Sea and Mediterranean Sea coasts.