Turning to our map once more, it will be seen that the wedge is not a regular one, but suggests rather the lower half of a human head, with the Lower Orinoco as the line of the jaw. The features are easily observed to separate the territory of the republic into four main divisions: (1) the Guayana Highlands, including all the region corresponding to the part of the head below the jaw-line, _i.e._, south and east of the Orinoco; (2) the great central area of plains or _Llanos_, bounded on the north and west by (3) the north-eastern branch of the great Andine chain, and in the north-west of the country (4) a smaller low-lying region round the Lake of Maracaibo. Each of these divisions includes somewhat varying types of land surface, but has its main features of uniform character. As already defined, the Guayana Highlands include the whole of that vast, more or less unexplored, tract of Venezuela lying on the right bank of the Orinoco and round the head-waters of that river. The area is primarily one huge elevated plateau about 1,000 feet or more above the sea, and from this rise a few principal mountain ranges, with some peaks over 8,000 feet high, while smaller hills and chains link up the larger systems. The highest ground is found on the Brazilian frontier, beginning at Mount Roraima (8,500 feet), where the three boundaries of Venezuela, British Guiana, and Brazil meet, and extends thence in the Sierras Pacaraima and Parima westward and southward to the head-waters of the Orinoco. From Roraima the Orinoco-Cuyuni watershed extends northward within Venezuela, along the Sierras Rincote and Usupamo and the Highlands of Puedpa, to the Sierra Piacoa, and thence south-east along the Sierra Imataca to the British limits again. The Sierra Maigualida forms the watershed between the Caura and the Ventuari. The whole area, which amounts to some 204,600 square miles, is well watered by the upper Orinoco and the Ventuari, with the other great tributaries, the Cuchivero, Caura, Aro, Caroni, and their affluents. Large as these rivers are, they are so broken by rapids that travel along them is only possible for much of their length in small portable craft, and even then the passage is fraught with danger. Save for the districts in the immediate neighbourhood of the Orinoco, and scattered areas elsewhere, the whole region is thickly covered with forests of valuable timber, containing rubber, tonka-beans, brazil-nuts, copaiba, and all the varied natural produce of the South American tropics.