The passes across the Himalaya, leading from Hindostan into Chinese Tartary, or rather into Western Thibet, more particularly between the rivers of Buspa and Schipke or Langzing Khampa, are from 2400 to 2900 toises, or 15346 to 18544 English feet. In the chain of the Andes I found the pass of Assuay, between Quito and Cuenca on the Ladera de Cadlud, having a similar elevation, being 2428 toises, or 15526 English feet, high. A great part of the mountain plains of the interior of Asia would be buried throughout the year in perpetual snow and ice, if it were not, that by the great radiation of heat from the Thibetian plateau, by the constant serenity of the sky, by the rarity of the formation of snow in the dry atmosphere, and by the powerful solar heat peculiar to the eastern continental climate, the limit of perpetual snow is wonderfully raised on the northern slope of the Himalaya,--perhaps to 2600 toises, or 16625 English feet above the level of the sea. Fields of barley (Hordeum hexastichon) are seen in Kunawur up to 2300 toises, or 14707 English feet; and another variety of barley called Ooa, and allied to Hordeum cœleste, even much higher. Wheat succeeds extremely well in the Thibetian highlands up to 1880 toises, or 12022 English feet. On the northern declivity of the Himalaya, Captain Gerard found the upper limit of the higher birch woods ascend to 2200 toises, 14068 English feet; and small bushes which serve the inhabitants for fuel to warm their huts, attain, in the latitude of 30-3/4° and 31° of north latitude, a height of 2650 toises (16945 English feet), or almost 200 toises (1279 English feet) higher than the limit of perpetual snow under the equator. From the data hitherto collected it would follow, that we may take the lower limit of perpetual snow on the northern side of the Himalaya, on the average, and in round numbers, at 2600 toises, or about 16600 English feet; whilst on the southern declivity of the Himalaya the snow-line sinks to 2030 toises, or about 13000 English feet. But for this remarkable distribution of temperature in the upper strata of the atmosphere, the mountain plain of Western Thibet would be uninhabitable to the millions who dwell there. (Compare my Examination of the Limit of Perpetual Snow on the two declivities of the Himalaya, in the Asie Centrale, T. ii. p. 435-437; T. iii. p. 281-326, and in Kosmos, Engl. ed. vol. i. note 403; S. 483 of the original.)