98 STEPPES AND DESERTS. 



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 

 18210 Parisian, or 19409 English feet, reached by Captain 

 Gerard, with seven barometers, on the mountain of Tarhi- 

 gang, a little to the north-west 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 23rd 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 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 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 35526 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 ot 

 the formation of snow in the dry atmosphere, and by the pov - 



