Dk. Thomson on the Climate and Vegetation of the Himalaya. 199 



tion has made sufficient progress in the mountains. These swampy tracts 

 are a series of lateral valleys -which run parallel to the base of the moun- 

 tains, and which, from being very slightly inclined, present great obsta- 

 cles to the escape of the water discharged into them by numerous streams 

 from the mountains. 



Along many parts of the Himalaya, a similar series of valleys nearly 

 parallel to the axis of the chain, but bounded externally by hills of from 

 2,000 to 4,000 feet in elevation, may be observed. These valleys are 

 known in the western Himalaya by the name of Dhuns. One of the 

 largest of them is the Deyra Dhun, well known to Indian travellers 

 as being traversed en route to Masuri a favourite hill station, and 

 now celebrated as the seat of an extensive cultivation of tea in a climate 

 which seems to suit admirably that valuable plant. The Deyra Dhiin is 

 in its centre or highest part, from which it slopes down both to east 

 and west towards the Ganges and Jumna, about 2,500 feet above the 

 level of the sea, or 1,500 feet above the level of the plains, immediately 

 outside of its bounding range. 



Other Dhuns occur all along the hills to the westward. They are 

 bounded on the north by the ancient rocks of the Himalaya, but on their 

 outer side always by the tertiary sandstones and conglomerates, now so 

 well known from the labours of Falconer and Cautley, as the Sewalik 

 formation. In the north of the Punjab there are often several series of 

 these valleys, the innermost only resting on transition rocks, the others 

 excavated out of the tertiary sandstones, which have there often a width 

 of from 30 to 50 miles. 



The vegetation of the low ranges of hills by which the Dhiins are 

 bounded externally, does not deviate much, if at all, from the tropical 

 type. They nowhere exceed an elevation of 4,000 feet, which is not 

 sufficient in isolated ridges, to bring about a sufficient change of mean 

 temperature, to produce much alteration in the vegetation. They are 

 only known, I believe, to the westward of Nepal, and therefore, in the 

 drier parts of the region, they are generally covered with trees the same 

 as those of the forest belt, with, in addition, a good deal of pinus longifolia, 

 a subtropical species of pine, and of a dwarf species of Phoenix, almost the 

 only palm of the western Himalaya. 



From these valleys where they exist, or from the open plains in other 

 cases, the exterior ranges of the Himalaya generally rise abruptly to a 

 height of 7,000 or 8,000 feet, in all parts of the chain, except at the 

 point of exit of the great rivers, where of course the outline of the moun- 

 tains is much modified. I shall ])robably better explain the structure of 

 the mass of mountains, by saying that the lateral chain which separates 

 any two adjacent river basins, generally terminates abruptly towards the 

 plains in a bold promontory 7,000 or 8,000 feet in height, from which 

 lateral branches parallel to the plains run in each direction, gradually 

 dimini.shing in elevation till they are terminated by the great rivers. 

 After the first sudden rise, the different ridges increase much more gra- 



Vol. 3.— No. 3. 5 



