By plateaus of the first class, we mean those high, continuous plains which lie at the elevation of more than from 4000 to 5000 feet above the sea level. The extreme height to which such plateaus rise is a fact yet to be ascertained. At an elevation of from 4000 to 5000 feet the highlands of the first class merge into those of the second. The point of transition is, of course, very difficult to fix with precision. The high plateaus of Asia rise more than 14,000 feet. They inclose the head-waters of the Ganges and the Indus. All central Asia is a vast congeries of highlands; but, as a body, they by no means belong to the most elevated of the globe. They are colossal in their length and breadth, but not in their uniform altitude. In the latter respect, they are far more varied than is generally supposed. The plateau of Thibet attains, in its whole great extent of 1800 miles in length and 500 miles in breadth, an average elevation of 10,800 feet above the sea level. In some cases it rises, of course, much higher, as, near the holy lake Manasarowar, for instance, where it is 14,000 feet above the sea. Others sink, as at Ladakh, in Little Thibet, to an altitude of about 9000 feet; so, too, Gertope, in the region remarkable for its goats and the rich shawls manufactured there, and Shiffke, are about 9804 feet above the sea. The plateau of Great Thibet, east of Lassa, the capital, and north of the Upper Brahmapootra or Yam-Dzangbotscha, is 9000 feet in elevation. There are also districts filled with mountain groups of great heights, but where the depressions sink to the level of the valleys of the Indus, Sutlej, Brahmapootra, as low indeed as 5460 feet, as at Cashmere, so that there is no lack of diversity in the great plateau of Thibet. The plateau of Mongolia, or more exactly the desert of Gobi, can be ranked only on its lower edges, where it touches the Chinese frontier, as of the first class, although in extent it is twice as large as the great plateau of Thibet. Only near the north bend of the Hoang-Ho and near Peking does it reach an altitude of 8000 feet, and gradually sinks away as it advances toward the northern frontier of the Chinese territory, to 5100 feet, and farther north to 4000 feet; in the middle portions of the great table-land it is depressed to a height of 2400 to 3600 feet; it rises again at the head-waters of the Orkhon and the Toola to an elevation of 4620 feet, and falls off in terraces toward Kiakhta, near the northern boundary, where it is 1330 feet high, Selenghinsk, on the Selenga, where it is 1632 feet high, and Berch-Udaisk, where it is 1458 feet high, till it reaches Lake Baikal, 1332 feet above the sea level according to Humboldt, though Erman makes it greater.