ILLUSTRATIONS (10). MOUNTAIN CHAINS OF ASIA. 73 



much higher. Wheat thrives admirably well in the Thibetian 

 highlands, up to an. elevation of 12,000 feet. On the 

 northern declivity of the Himalaya, Captain Gerard found 

 that the upper limits of the birch woods ascend to 14,069 

 feet; and small brushwood used by the natives for fuel 

 in their huts is even found within the parallels of 30 45 ; 

 and 31 north latitude, at an elevation of 16,946 feet, and 

 therefore nearly 1280 feet higher than the lower snow-limit 

 in the equatorial regions. It follows from the data hitherto 

 collected that on the northern declivity of the Himalaya 

 the mean of the lower snow-line is at least 16,626 feet, 

 whilst on the southern declivity it falls to 12,980 feet. But 

 for this remarkable distribution of heat in the upper strata 

 of the atmosphere, the mountain plain of Western Thibet 

 would be rendered uninhabitable for the millions of men 

 who now occupy it.* 



In a letter which I have lately received from India from 

 Dr. Joseph Hooker, who is engaged in meteorological and 

 geological observations, as well as in the study of the geo- 

 graphy of plants, he says, "Mr. Hodgson, whom we here 

 consider more thoroughly conversant than any other geo- 

 grapher with the hypsometric relations of the snow ranges, 

 recognises the correctness of the opinions you have advanced 

 in the third part of your Asie centrale, regarding the cause 

 of the unequal height of the limit of perpetual snow on the 

 northern and the southern declivity of the Himalaya range. 

 In the trans- Sutledge region (in 36 north latitude) we 

 often observed the snow limit as high as 20,000 feet, 

 whilst in the passes south of Brahmaputra, between Assam 

 and Birmah (in 27 north latitude), where the most southern 

 snow-capped mountains of Asia are situated, the snow limit 

 sinks to 15,000 feet." I believe we ought to distinguish 

 between the extreme and the mean elevations, but in both 

 we find the formerly disputed difference between the Thi- 

 betian and the Indian declivities manifested in the clearest 

 manner. 



* Compare my investigation regarding the snow-limit on both declivi- 

 ties of the Himalaya in my Asie centrale, t. ii., pp. 435 437; t. iiL., 

 pp. 281326; and in Cosmos, vol. i., p. 337, Bonn's ed. 



