No portion of the so-called Desert of Gobi, which consists in part of fine pasture lands, has been so thoroughly investigated in relation to its differences of elevations as the zone which extends over an area of nearly 600 miles, between the sources of the Selenga and the Chinese wall. A very accurate barometrical levelling was executed, under the auspices of the Academy of St. Petersburgh, by two distinguished savans—the astronomer George Fuss, and the botanist Bunge. They accompanied a mission of Greek monks to Pekin, in the year 1832, in order to establish there one of those magnetic stations whose construction I had recommended. The mean height of this portion of the Desert of Gobi amounts hardly to 4263 feet, and not to 8000 or 8500 feet, as had been too hastily concluded from the measurements of contiguous mountain summits by the Jesuits Gerbillon and Verbiest. The surface of the Desert of Gobi is not more than 2558 feet above the level of the sea between Erghi, Durma, and Scharaburguna; and scarcely more than 320 feet higher than the plateau of Madrid. Erghi is situated midway, in 45° 31′ north lat., and 111° 26′ east long., in a depression of the land extending in a direction from south-west to north-east over a breadth of more than 240 miles. An ancient Mongolian saga designates this spot as the former site of a large inland sea. Reeds and saline plants, generally of the same species as those found on the low shores of the Caspian Sea, are here met with; while there are in this central part of the desert several small saline lakes, the salt of which is carried to China. According to a singular opinion prevalent among the Mongols, the ocean will at some period return, and again establish its dominion in Gobi. Such geological reveries remind us of the Chinese traditions of the _bitter lake_, in the interior of Siberia, of which I have elsewhere spoken.[BF]