That outside of the Thibetian highlands and of the Gobi, the boundaries of which have been defined above, there are in Asia, between the parallels of 37° and 48°, considerable depressions and even true lowlands, where one boundless uninterrupted plateau was formerly imagined to exist, is shewn by the cultivation of plants which cannot thrive without a certain degree of heat. An attentive study of the travels of Marco Polo, in which the cultivation of the vine and the production of cotton in northern latitudes are spoken of, had long called the attention of the acute Klaproth to this point. In a Chinese work, entitled “Information respecting the recently-subdued Barbarians (Sin-kiang-wai-tan-ki-lio),” it is said, “the country of Aksu, somewhat to the south of the Celestial Mountains (the Thian-schan), near the rivers which form the great Tarim-gol, produces grapes, pomegranates, and numberless other excellent fruits; also cotton (Gossypium religiosum), which covers the fields like yellow clouds. In the summer the heat is exceedingly great, and in winter there is here, as at Turfan, neither severe cold nor heavy snow.” The district round Khotan, Kashgar, and Yarkand, still pays its tribute in home-grown cotton as it did in the time of Marco Polo. (Il Milione di Marco Polo, pubbl. dal Conte Baldelli, T. i. p. 32 and 87.) In the Oasis of Hami (Khamil), above 200 miles east of Aksu, orange trees, pomegranates, and vines whose fruit is of a superior quality, grow and flourish. The products of cultivation which are thus noticed imply the existence of only a small degree of elevation, and that over extensive districts. At so great a distance from any coast, and in those easterly meridians where the cold of winter is known to exceed that of corresponding latitudes nearer our own part of the world, a plateau which should be as high as Madrid or Munich might indeed have very hot summers, but would hardly have, in 43° and 44° latitude, extremely mild winters with scarcely any snow. Near the Caspian, 83 English feet below the level of the Black Sea, at Astrachan in 46° 21′ lat., I saw the cultivation of the vine greatly favoured by a high degree of summer heat; but the winter cold is there from -20° to -25° Cent. (-4° to -13° Fahr.) It is therefore necessary to protect the vines after November, by sinking them deep in the earth. Plants which live, as we may say, only in the summer, as the vine, the cotton bush, rice, and melons, may indeed be cultivated with success between the latitudes of 40° and 44° on plains of more than 500 toises (3197 English feet) elevation, being favoured by the powerful radiant heat; but how could the pomegranate trees of Aksu, and the orange trees of Hami, whose fruit Père Grosier extolled as distinguished for its goodness, bear the cold of the long and severe winter which would be the necessary consequence of a considerable elevation of the land? (Asie Centrale, T. ii. p. 48-52,