East and south of this mountainous country is the vast region, thinly populated and not well known, of the great Orinoco Basin, occupying three fourths of the country; first come the llanos, followed by a forested district, with hilly, mountainous country beyond. The llanos, covering 87,000 square miles on the north side of the great river, are grassy plains broken by islands of trees. Near the mountains north and west are extensive forests. The llanos are of slightly varying altitude, in parts rising imperceptibly, but often by terraces or banks a few feet high. In the western section there are large tracts in the Portuguesa Valley but 300 feet above the sea; in other places the land rises to 650 feet, and to a still greater height on the mesas which form the watershed between the Orinoco and the rivers Unare and Aragua flowing into the Caribbean Sea. THIRD SECTION South and east of the Orinoco River are the Guiana Highlands, said to cover 200,000 square miles, for the most part a plateau 1000 feet and upwards in elevation, from which rise several mountain chains connected by lower hills, the Parime Range separating the Orinoco and Amazon Basins. A few peaks rise 8000 feet; the highest known is Mt. Roraima, 8500 feet, at the southeast corner, where the boundaries of British Guiana, Brazil, and Venezuela come together. FOURTH SECTION This region, much smaller, occupies the northwest part of the Republic, which may be considered as a coastal plain. It includes the alluvial area around Lake Maracaibo, the Coro and the Paraguana lowlands, with open sandy hills extending along the shore of the Gulf of Venezuela to the end of the Paraguana Peninsula, and some islands of the same character. The Lake district is somewhat similar to the Orinoco Delta, with many rivers coming in at the south, and with open lagoons and swamps; it is bordered by dense forests often inundated by rains. East and west towards the north between the swamps are higher lands with some grassy plains. At the west is the Sierra de Perija on the Colombian frontier. RIVERS AND LAKES Venezuela is said to have 72 large and more or less navigable rivers, of which the Orinoco is the chief. Its length, variously stated, may be 1570 miles and the area of its basin 370,000 square miles. The =Orinoco=, rising near the Brazilian boundary, first flows northwest, then northerly forming the boundary line with Colombia, and from the entrance of the Meta River, northeast and east to the Atlantic Ocean. Its low forested delta covers 8500 square miles. Boca de Navios, the largest mouth, is 20 miles wide with a depth of 17 feet at the bar. Among the 400 or more tributaries the most important are the Caroni, the Caura, and the Ventuari, draining the mountainous and forested section at the south; and the Guaviare, Vichada, Meta, and Apure coming in from the west, the first three from Colombia. The Casiquiare, previously mentioned, connects the Orinoco with the Rio Negro.