The _Pine Plains_ are a district of sandy alluvion, bounded by the gravelly soil of Guilderland and Duanesburgh on the south-west, and by the river alluvions of Niskayuna and Watervliet, on the north-east, and covering an area of about seventy square miles. This tract is included in a triangle formed by the junction of the Mohawk with the Hudson, and of which the Helleberg, a lofty chain of highlands, visible from the plains at the distance of twenty miles, forms the south-western boundary. Situated near the centre of a state, computed at forty thousand square miles, and containing a population of nearly two million souls, this tract presents the topographical novelty of an unreclaimed desert, in the heart of one of the oldest counties in the state, and in the midst of a people characterized for enterprise and public spirit. Several attempts have lately been made to bring this tract into cultivation, and from the success which has attended the introduction of gypsum, and other improved modes of agriculture, it is probable the whole will, at some future period, be devoted to the cultivation of the various species of grasses, fruit trees, and esculent roots; three branches of agriculture to which its sandy soil seems admirably adapted. GENERAL REMARKS ON PLAINS AND PRAIRIES. Plains like valleys are of two classes; the high plains, which are found between two chains of mountains, are frequently of great extent, and are placed as it were upon the shoulders of secondary mountains; such are the elevated plains of Tartary, of Persia, and probably of the interior of Africa. The plains of Quito are twelve thousand feet above the level of the sea; those of Karakorum, in Chinese Mongolia, are probably as elevated. The low plains, whose soil is composed of sand, gravel and shells, seem formerly to have been the basins of interior seas. Such are the plains on the north side of the Caspian, the large plain to the south of the Baltic, and that through which the river of the Amazon flows; the Tehama of Arabia, the Delta of Egypt, and others of a similar nature, which seem to have been once covered by the waters of the ocean and its gulfs. The immense plains covered with grass, called _prairies_ in the United States, are the _steppes_ of Asia, and the _pampas_ of South America. CHAPTER IV.――RIVERS. ALL the rivers of the United States, of the first magnitude, have their sources, either in the Rocky Mountains, or in elevated spurs projecting from the sides of that range. Many of the rivers which descend from the western sides of the Alleghanies are of inconsiderable volume, and by no means remarkable for the rapidity or the directness of their course. Those which flow from the eastern and southern sides of these mountains are worthy of extended description, even in the same pages with the great tributaries of the Mississippi. They afford the advantages of a good inland navigation to most parts of the states.