Geologically, Sri Lanka is composed of gneiss, schist, granite, quartzite and crystalline limestone-an agglomerative, quartzite rich gemstone deposits, washed by streams and rivers from the central highlands in to lowland valleys. For more than 2000 years Sri Lanka has been a noted producer of rubies, sapphires, and semiprecious stones such as amethyst, alexandrite and topaz. From a coastal plain, the island rises to an area of South-Central highlands, which reach their highest point at Pidurutalagala (2524m/ 8281ft. Two major rivers flow out of the highlands - the Mahaweli, which flows North-East to reach the Indian Ocean near Trincomalee, and the Walawe, which joins the ocean near Hambantota on the South coast. A third, the Aruvi, flows out of the Northern fringes of the highlands and the dry zone which surrounds them, emptying into Palk Bay on the Northwest coast.