CLIMATE OF HIMALAYA. 249 



dual, but also, so far as our present ratlier limited number of ob- 

 servations go, very regular. The effects of the south-west or 

 rainy monsoon diminish step by step, as we advance westward, 

 till on arriving at the valley of the Indus at the western extre- 

 mity of the Himalaya, it ceases to be observed at all. In these 

 most western portions of the chain, very little rain falls at any 

 season of the year, and the little which does occur falls in the 

 spring months, and is therefore quite independent of the regular 

 monsoon. 



It is also worthy of note, that in the more western parts of the 

 chain the climate is extremely dry at all periods of the year, 

 except during the monsoon or rainy season, as it is called in 

 India, while to the eastward the climate of the mountains shares 

 to a considerable extent the more equable and always moist cli- 

 mate of Bengal. 



The most important point of all, however, regarding the cli- 

 mate in respect of its effects on vegetation, which requires to be 

 borne in mind, is that a very great portion of the rain which falls 

 is deposited on the first range of mountains upon which the rain 

 wind strikes. I have already pointed out that this is the case 

 with the Khasya range, and it is there highly strikingly illus- 

 trated by the fact, that it is only on tlie very south side of the 

 hills that the rain-fall is so enormous, the fall twenty miles north 

 of Churra being probably less than half what it is there. 



This tendency of the rain-fall to exhaust itself very consider- 

 ably on the first range of mountains to which it has access, is 

 peculiarly important in a mountain chain 150 miles in width, its 

 effect being that tlie upper part of all the large valleys, and espe- 

 cially the interior valleys and their ramifications, are much more 

 dry than those adjacent to the plains of India. Even in the most 

 humid part of the Himalaya, in Sikkim, this difference is ex- 

 tremely marked, and in the more dry parts to the west, (the 

 extreme east interior is not known,) the inner valleys are so dry 

 tliat rain is scarcely ever known to fall. 



In close connection with the increase of aridity, as we advance 

 from the plains of India to the interior of the mountains, I may 

 mention the increased elevation of the line of perpetual congela- 

 tion, which has evidently the same cause. In the outer lofty 

 ranges of the Himalaya, the snow line is met with at about 

 16,000 feet, while in the Tibetan part of the chain many ridges 

 of 20,000 feet of elevation are almost entirely bare of snow. 



Having thus alluded in very brief and general terms to the 

 most prominent physical features of the mountain chain of Hima- 

 laya, I shall proceed to describe, as rapidly as is consistent with 

 clearness, the general character of the vegetation which is to be 

 observed in its different parts at all elevations, from the plains of 



