America possesses a number of plateaus of the first class. To the most prominent of these belong the ones which were first thoroughly studied by Alexander von Humboldt. It is to him that we owe our first accurate impressions of table-lands which, before his day, had been indiscriminately confounded with mountains, and had had no place assigned to them in the department of Geography. Doubtless, too, great prominence was given to plateaus at the outset; they were pushed into unseemly proportion to other matters as well worthy of investigation, but they have come into their true place, and now only wait the development of new facts regarding the size and height of some, to be properly understood and appreciated. The measurements made in North, Central, and South America give the following results; much more complete, it may be remarked, than the results yet gained in Asia and Africa. To the plateaus of the first class belong in America, at latitude 0°, the plain of Quito, almost 9000 feet above the sea, (Los Pastos in the north being near 11,000 feet,) and to the south, at 17° south latitude, the plateau of Upper Peru. Here the great Lake Yiticaca is found, 12,000 feet above the sea; eastward of the lake, the table-land rises yet higher, and at Alto de Toleda it is 14,000 feet in elevation, as high as the highest part of Thibet. At 20° south latitude, south of Lake Yiticaca, is the City of Potosi, whose streets are 12,822 feet above the Pacific. In Central America is found, at 20° north latitude, the extended table-land of Mexico, 500 miles wide, rising to a height of 7000 feet, and farther to the north, in New Mexico, the plateau of Santa Fé, 35° north latitude east of the Rocky Mountains, and 7100 feet above the sea. The table-land on the west side of the mountains, and toward the Great Salt Lake, is undoubtedly just as elevated. Europe and Australia are wanting in plateaus of the first rank, and in general the whole immense flat northern districts of the globe, though we are not yet quite familiar enough with the extreme north of America to speak with entire confidence regarding it. _Plateaus of the Second Class._ Elevated plains which are at once continuous and bounded by a definite line of demarkation, and which do not attain an altitude of more than 4000 or 5000 feet, are considered plateaus of the second class. They are far more general over the whole earth than plateaus of the first class; in every one of the great divisions of the globe they appear in the utmost possible diversities of elevation, sometimes so gradually ascending that the lowest limit is hardly to be perceived. This makes it not only expedient but necessary to assign to plateaus a fixed though arbitrary system of classification, for without it we could attain to no thorough view of all their relations. This general system must afterward be confirmed and justified by protracted special investigations.