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Show 92 STEPPES AND DESERTS. than in any of the other mountains), might prove very deceptive in the temperate zone of Thibet, where radiation is so active in the table-land, and where the lower limit of perpetual snow does not form a regular line at an equal elevation, as it does in the tropics. The greatest elevation above the level of the sea ever attained by human beings on the declivity of the Himalaya, is 3035 toises, or 18,210 Parisian, or 19,409 English feet, reached by Captain Gerard, with seven barometers, on the mountain of Tarhigang, a little to the northwest of Schipke. (Colebrooke, in the Transactions of the Geological Society, vol. vi. p. 411.) This happens to be exactly the same height as that reached by myself on the 23d of June, 1802, and thirty years later by my friend Boussingault, on the 16th of December, 1831, on the declivity of the Chimborazo. The unattained summit of the Tarhigang is, however, 197 toiscs, or 1260 English feet higher than that of the Chimborazo. 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 15,346 to 18,544 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 15,526 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, ~f 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 sola.r 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 16,625 English feet above the level of the sea. Fields of barley (Hordeum hexastichon) are seen in Kunawur up to 2300 toises, or 14,707 English feet; and another variety of barley called Ooa, ancl allied to Hordeum coe!este, even much higher. Wheat succeeds extremely well in the Thibetian highlands up to 1880 toiscs, or 12,022 English feet. On the northern declivity of the Himalaya, Captain Gerard found the upper limit of the higher birch woods ascend to 2200 toises, 14,068 English feet; and small |