394 PHYSICAL GEOGEAPHY OF SIKKIM. Appendix E. 



Tibetan mountains impinges against the side facing the north, which 

 is hence more bare of vegetation. An infinite number of local 

 peculiarities will suggest themselves to any one conversant with 

 physical geography, as causing unequal local distribution of light, 

 heat, and moisture in the different valleys of so irregular a country ; 

 namely, the amount of slope, and its power of retaining moisture 

 and soil ; the composition and hardness of the rocks ; their dip and 

 strike ; the protection of some valleys by lofty snowed ridges ; and 

 the free southern exposures of others at great elevations. 



The position and elevation of the perpetual snow * vary with 

 those of the individual ranges, and their exposure to the south wind. 

 The expression that the perpetual snow lies lower and deeper on the 

 southern slopes of the Himalayan mountains than on the northern, 



* It appears to me, as I have asserted in the pages of my Journal, that the 

 limit of perpetual snow is laid down too low in all mountain regions, and that 

 accumulations in hollows, and the descent of glacial ice, mask the phenomenon 

 more effectually than is generally allowed. In this work I define the limit, as is 

 customary, in general terms only, as being that where the accumulations are very 

 great, and whence they are continuous upwards, on gentle slopes. All perpetual 

 snow, however, becomes ice, and, as such, obeys the laws of glacial motion, 

 moving as a viscous fluid ; whence it follows that the lower edge of a snow-bed 

 placed on a slope is, in one sense, the termination of a glacier, and indicates a 

 position below that where all the snow that falls melts. I am well aware that it 

 is impossible to define the limit required with any approach to accuracy. Steep 

 and broken surfaces, with favourable exposures to the sun or moist winds, are 

 bare much above places where snow lies throughout the year ; but the occurrence 

 of a gentle slope, free of snow, and covered with plants, cannot but indicate a 

 point below that of perpetual snow. Such is the case with the " Jardin " on the 

 Mer de Glace, whose elevation is 9,500 feet, whereas that of perpetual snow is 

 considered by Professor J. Forbes, our best authority, to be 8,500 feet. Though 

 limited in area, girdled by glaciers, presenting a very gentle slope to the east, 

 and screened by surrounding mountains from a considerable proportion of the 

 sun's rays, the Jardin is clear, for fully three months of the year, of all but 

 sporadic falls of snow, that never lie long ; and so are similar spots placed higher 

 on the neighbouring slopes ; which facts are quite at variance with the supposition 

 that the perpetual snow-line is below that point in the Mont Blanc Alps. On 

 the Monte Rosa Alps, again, Dr. Thomson and I gathered plants in flower, above 

 12,000 feet, on the steep face of the Weiss-thor Pass, and at 10,938 feet on 

 the top of St. Theodule ; but in the former case the rocks are too steep for any 

 snow to lie, they are exposed to the south-east, and overhang a gorge 8000 feet 

 deep, up which no doubt warm currents ascend ; while at St. The'odule the plants 

 were growing on a slope which, though gentle, is black and stony, and exposed to 

 warm ascending currents, as on the Weiss-thor ; and I do not consider either of 

 these as evidences of the limit of perpetual snow being higher than their position. 



