GEORGETOWN, Guyana. The capital city of Guyana, Georgetown is also the nation's chief port. Located on the Atlantic Ocean, on the northern coast of South America at the mouth of the Demerara River, Georgetown is the main commercial and manufacturing center of Guyana. It exports sugar, rice, and tropical fruits as well as timber, balata (a product made by drying tree juices), bauxite, gold, and diamonds. Large sugar refineries are located in the city. There is a botanical garden, a zoo, a seaside promenade, and many outdoor recreational facilities. Guyana's highway network is poor, though roads lead along the coast and inland from Georgetown for a short distance. The city is served by various international steamship lines and airlines. A railroad, claimed to be the oldest in South America, runs along the coast from Georgetown to a point opposite New Amsterdam.      Public buildings in the center of the city include the government offices, town hall, cathedral, and educational institutions, which include the University of Guyana. Many of Georgetown's houses and public buildings are made of wood, but most business offices are reinforced concrete.      The settlement was founded by the British in 1781 and named after George III. It was largely rebuilt by the French by 1784 and, known as Stabroek by Dutch colonists, the seat of government of the combined colonies of Essequibo and Demerara. When the British regained control in 1812, the name was changed back to Georgetown. Population (1976 estimate), 72,049.