INTRODUCTION. 3 J? 



iife in a zone that is nearly 3000 feet lower than that to whict 

 it attains in the equinoctial region of the Cordilleras. 



fJateau, this limit is at 16,625 feet from 30^° to 32° of latitude, whik 

 at the equator, iu the Audes of Quito, it is^5,790 feet. Such is the 

 result I have deduced from the combiuatiou of numerous data furnished 

 by Webb, Gerard, Herbert, and Moorcroft. (See my two memoirs on 

 the mountains of India, in 1816 and 1820, in the Ann. de Chisnie et tU 

 Physique^ U iii., p. 303; t. xiv., p. 6^ 22, 50.) The greater elevation to 

 which the limit of perpetual snow recedes on the Tartarian dechvity 

 is owing to the radiation of heat from the neighboring elevated plains, 

 to the purity of the atmosphere, and to the infrequent formation of snow 

 in an air which is both very cold and very dry. (Humboldt, Asie Cen 

 trale, t. iii., p. 281-326.) My opinion ou the ditFerence of height of 

 tlie snow-hne on the two sides of the Himalaya has the high authority 

 of Colebrooke iu its ^vor. He wrote to me in June, 1824, as follows: 

 *' I also find, from the data in my possession, tliat the elevation of the 

 line of perpetual snow is 13,000 feet. On the southern declivity, and 

 at latitude 31°, Webb's measurements give me 13,500 feet, consequently 

 500 feet more than the height deduced from Captain Hodgson's ob 

 servations. Gerard's measurements fully confirm your opinion iha- 

 the line of snow is higher on the northern than on the southern side.' 

 U was not until the present year (1840) that we obtained the complete 

 tnd collected journal of the brothers Gerard, published under the su 

 pervision of Mr. Lloyd. (Narrative of a Journey from Cawnpoor t 

 the Boorendo Pass, in the Himalaya, by Captain Alexander Gerard ant 

 John Gerard, edited by George Lloyd, vol. i., p. 291, 311, 320, 327, au( 

 ;i41.) Many interesting details regarding some localities may be found 

 in ttie narrative of A Visit to the Shatool,for the Purpose of determining 

 the Line of Perpetual Snow on the southern face of the Himalaya, in At 

 gust, 1822. Unfortunately, however, these travelers always confoun' > 

 the elevation at which sporadic snow falls with the maximum of th 

 height that the snow-line attains on the Thibetian plateau. Captaiti 

 Gerard distinguishes between the summits tliat rise in the middle o 

 the plateau, where he states the elevatioi^ of the snow-line to be hi 

 ♦ween 18,000 and 19,000 feet, and the northern slopes of the chain o 

 Uie Himalaya, which border on the defile of the Sutledge, and can n 

 liate but little heat, owing to the deep ravines with which they ar . 

 intersected. The elevation of the village of Tanguo is given at only 

 )300 feet, while that of the plateau surrounding the sacred lake of Mm 

 •lasa is 17,000 feet. Captain Gerard finds the snow-line 500 feet lowt j 

 on the northern slopes, where the chain of the Himalaya is broke i. 

 through, than toward the southern declivities facing Hindostan, and h t 

 ':here estimates the line of perpetual snow at 15,000 feet. The moi i 

 striking differences are presented between the vegetation on the Thil 

 etian plateau and that cliaracteristic of the southern slopes ot the Hin 

 .ilaya. Ou the latter the cultivation of grain is arrested at 9974 feet, 

 and even there the corn has often to be cut when the blades are stiil 

 green. The extreme limit of forests of tall oaks and deodars is 11,960 

 feet ; that of dwarf birches, 12,983 feet. On the plains, Captain Gerard 

 found pastures up to the height of 17,000 feet; the cereals will grow t.t 

 14,100 feet, or even at 18,540 feet; birches with tall stems at 14,100 

 feet, and copse or brush wood applicable for fuel is found at an eleva 

 tion of upward of 17,000 feet, that is to say, 1280 feet above the lowej 

 iimito of the snow-liije at the equator, in the province of Quito. It is 



