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 Geo- 

 logical 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 unat- 

 tained summit of the Tarhigang is, however, 197 toises, 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 Kharnpa, 

 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 ^md Cuenca, on the Ladera de Cadlud, having a similar ele- 

 vation, 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, 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 won- 

 derfully 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 bar- 

 ley called Ooa, and allied to Hordeum creleste, even much higher. 

 Wheat succeeds extremely weir in the Thibetian highlands up to 

 1880 toises, 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 



