86 Cr.IMATK AND VEGETATION OF 



or not on the line of section) ; the upper represents a parallel 

 ridge, of greater mean elevation, further west, introduced to 

 show the maximum elevation of the Silikim mountains, Kin- 

 chinjunga (28,178 feet) (K) being represented on it. A deep 

 valley is interposed between these two ridges, with a feeder of the 

 Teesta in it, which runs south from Kinchin, and turning west 

 enters the Teesta at R. The position of the bed of the Teesta 

 river is indicated by a dotted line from its source at T to the 

 plains at S ; of Darjiling, on the north flank of the outer range, 

 by D ; of the first point where perpetual snow is met with, by 

 P ; and of the first indications of a Tibetan climate by C. 



A warm current of air, loaded ^nth vapour, will deposit the 

 buliv of its moisture on the ridge (8000 feet) D. Passing on, 

 little \^ill be precipitated on E, whose elevation is the same as 

 that of D, but much at F (10,000 feet), where the current being 

 further cooled has less capacity for holding vapour than it had at 

 D, and is ftirther exhausted. "When it ascends to P (15,000 

 feet) it is sufficiently cooled to deposit snow in the winter and 

 spring months, more of which falling than can be melted during 

 the summer, it becomes perennial. At K (20,000 feet) ver}- little 

 falls, and it is doubtful if the southerly current ever reaches the 

 prodigiously elevated isolated summit of Kinchinjunga (28,178 

 feet) ;* but all that does, is evaporated or retained as snow. The 

 amount of surface above 20,000 feet is, however, too limited and 

 broken into isolated peaks to drain the already nearly exhausted 

 wind current, whose condensed vapours roll along in fog beyond 

 K, are dissipated during the day over the arid mountains of 

 Tibet, and deposited at night on the cooled surface of the 

 earth. 



Other phenomena of no less importance than the distribution 

 of vapour, and more or less depending on it, are the duration 

 and amount of solar and terrestrial radiation. Towards S the 

 sun is rarely seen during the rainy season, as well from the con- 

 stant presence of nimbi aloft, as of fog on the surface of the 

 ground. An absence of both light and heat is the result in the 

 parallel of K ; and at C low fogs prevail at the same season, 

 but do not intercept either the same amount of light or heat ; 

 whilst at T there is much sunshine and bright light. During 

 the night, again, there is no terrestrial radiation between S 

 and P ; the rain either continues to pour — in some months 

 with increased violence — or the saturated atmosphere is con- 



* I believe that the utmost elevation the S.E. monsoon attains is 23,000 

 feet, and that only where the whole mass of land is immensely elevated. 

 A perennial westerly wind appears by the clouds' motions to blow at the top 

 of Kinchiniunga. 



