INTRODUCIION. 31 



iif(i in a zone that is nearly 3000 feet lower than that to whicJ 

 :t attains in the equinoctial region of the Cordilleras. 



pkteau, this Umit is at 16,625 feet from 30$° to 32° of latitude, whili 

 at the equator, iu the Andes of Quito, it is 15,790 feet. Such is the 

 resuh I have deduced from the combination of numerous data fm'nished 

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

 the mountains of India, iu 1816 and 1820, in the Ann. de Chimie et dU 

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

 which the limit of perpetual snow recedes on the Tartarian declivity 

 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 on the ditference of height of 

 the snow-line on the two sides of the Himalaya has the high authority 

 of Colebrooke in its favor. He wrote to me in June, 1824, as follows: 

 " I also find, from the data in my possession, that 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 

 aervations. Gerard's measurements fully confirm your opinion tha' 

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

 It was not until the present year (1840) that we obtained the complet« 

 und collected journal of the brothers Gerai'd, published under the su 

 pervisiou of Mr. Lloyd. {Narrative of a Journey from Cawnpoor tt 

 the Boor endo Pass, in the Himalaya, by Captain Alexander Gerard ami 

 John Gerard, edited by George Lloyd, vol. i., p. 291, 311, 320, 327, an«i 

 ^Hl.) Many interesting details regarding some localities may be founiil 

 in the nan-ative of A Visit to the Shatool,for the Purpose of determifiini? 

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

 gust, 1822. Unfortunately, however, these travelers always confound 

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

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

 Gerard distinguishes between the summits that rise in the middle oi 

 the plateau, where he states the elevation of the snow-line to be hx< 

 tween 18,000 and 19,000 feet, and the northern slopes of the chain ol 

 the Himalaya, which border on the defile of the Sutledge, and can rxv 

 diate but little heat, owing to the deep ravines with which they ai e 

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

 9300 feet, while that of the plateau surrounding the sacred lake of Mii- 

 nasa is 17,000 feet. Captain Gerard finds the snow-line 500 feet lowti 

 on the northern slopes, where the chain of the Himalaya is broken 

 through, than toward the southern declivities facing Hindostan, and fc e 

 there estimates the line of perpetual snow at 15,000 feet. The mout 

 striking differences are presented between the vegetation on the Thil»- 

 etian plateau and that characteristic of the southern slopes ot the Him- 

 al.aya. 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 still 

 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 jit 

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

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

 tioa of upward of 17,000 feet, that is to say, 1280 feet above the lower 

 limits of the snow-line at the equitor. in the province of Quito. It is 



