202 Dr. Thomson on the Climate and Vegetation of the Himalaya. 



5,000 feet, but on the more exposed slopes, plants of warm climates ex- 

 tend up ],000 feet higher, and the herbaceous vegetation, principally 

 grasses, is entirely composed of ti-opical forms. 



It is only on approaching Simla, and attaining a lieight of nearly 7,000 

 feet, that forest vegetation commences; at that elevation, open foreots of 

 oak. Rhododendron, and Andromeda, intermixed with several species of 

 pines, and a great number of temperate shrubs, of such genera as Rosa, 

 Rubus, Viburnum, Berberis, Spiraea, Lonicera, Indigofera, Prinsepia, 

 Salix, Daphne, and others. 



The view from Simla presents a very marked contrast with that from 

 Darjiling. The general outline of the mountains is very much the same, 

 but they are more rocky, and very generally bare; the forests, which to the 

 north are dense and abundant, occupying chiefly the north slopes of the 

 mountains, so that in looking from the south the crest of the ridges only 

 are seen to be wooded. The scenery, therefoi-e, is more diversified than 

 in the eastern Himalaya, and abstracting the snowy mountains, more 

 pleasing to the eye. 



Between the two extremes which I have described, every intermediate 

 form may of course be met with, the law of alteration being apparently 

 the following, that in advancing westward towards less humid climates, the 

 lower hills from about 6,000 to 2,000 feet, become more and more bare and 

 grassy, while the lower levels and the base of the mountains retain a greater 

 degree of damp and are clothed with forest. It woidd appear also that 

 above 6,000 or 7,000 feet, up to 10,000 or 11,000 feet, at which eleva- 

 tion mountain ranges sensibly interrupt the passage of the moist atmo- 

 sphere, the temperate ranges are more moist than those below them, which 

 do not collect the clouds, and have a higher temperature, and consequently 

 more powerful sun. To the eastward of Sikkim, the same phenomena 

 are very well marked, the lower ranges being extremely dry and arid, 

 while above 7,000 feet, dense forest and a humid atmosphere prevail, just 

 as in the mountains of Sikkim. 



The valleys of the larger rivers which traverse the Himalaya fi'om 

 north to south, have of course a much lower elevation than the mountains 

 by which they are surrounded; and up them, therefore, tropical vegetation 

 penetrates very far into the interior. In the extreme west, the valleys 

 of the Indus and Chenab, and even of the Sutlej, are up to the height of 

 5,000 feet, which they do not attain till more than 100 miles from their 

 exit into the plains, hot, dry, and tropical. Further east, the tropical 

 forest stretches far up the vallies, and they are only bare for a small por- 

 tion of their extent, and in the humid atmosphere of Sikkim they are 

 densely wooded throughout. In that province, the valleys of the Teesta 

 and its tributaries, carry tropical vegetation far into the interior, almost 

 within a day's journey of the line of perpetual snow, and the luxuriance 

 of the dense and dripping forest requii'es to be seen to be understood. 



The temperate region of the Himalaya may be said to extend from 

 about 5,000 feet, or a little above it, to the upper limit of arboreous vege- 



