The navigation of both these river systems, the Amazon and the River Plate, is limited or rather interrupted by the fourth great feature of the continent, the Brazilian plateau. The Paraná and its affluents plunge from this plateau to the southern plain in tremendous waterfalls. The southern tributaries of the Amazon pierce their way down into the Amazonian valley along defiles, cataracts and rapids sometimes extending scores of miles. The Amazonian affluents are mostly navigable from the main river to the foot of these cascades. Above the cascades, there stretch fresh reaches of navigable water, providing many paths into the far interior. Similar conditions are found on the two branches of the River Tocantins and on other Brazilian rivers, such as the São Francisco and the Paranahyba. With the future growth of population, the construction of lateral railways and, later, perhaps the partial canalisation of rivers, there is no limit to the possibilities of internal water communication. The wealth of water power which awaits application is obvious. As to possibilities of water storage and irrigation, it suffices to say that on the Lower Orinoco and also on the Lower Amazon the difference of water level between wet and dry seasons is at least fifty feet, and most of the affluents rise and fall proportionately. The great Brazilian plateau, which has just been mentioned, further justifies the description of South America as the fertile continent--the region of habitable tropics. The vast scale of this plateau and its relation to the River Plate system justify its description here as a continental feature rather than a purely national feature, although it is mainly a national possession of Brazil. From the north-east shoulder of the Brazilian coast, this varied plateau, seamed by many clefts, stretches southwards and south-westward in a vast semi-circular sweep dividing the two river-systems. The Paraná and its affluents plunge from this plateau towards the south and west. Northwards and eastwards it sends a multitude of streams to the Amazon and the Atlantic. These Brazilian uplands naturally vary in character and productiveness, but they are in great part suitable for white habitation and especially for the grazing of cattle. There is no winter; there is little of excessive or torrid heat; the grass grows all the year round; and in the neighbourhood of some rivers, the grasslands are annually renovated by seasonable and shallow floods. _Political Distribution_