28 BOTANICAL INFORMATION. 
lat. 27° 30. I have seen well-defined patches quite exposed, lower 
down on the south flanks of Kinchin. Glaciers abound, but not to- 
wards the southern limits of the perpetual snow, where the mountains 
are too rugged. 
It is a remarkable fact that every river-valley I have ascended opens 
out, and is broad and flat-floored at about 10,000 feet: it becomes 
imperceptibly more and more so, in ascending; and as it conducts you 
beyond the limits of clouds, rain, and snow, it gradually assumes 
a dryer, barren, and more Thibetan character. 
The average rain-fall at Darjeeling is 120 inches, and it is progres- 
sively less in the interior, till the mountains reach 15,000 feet, and 
then it suddenly diminishes in quantity. 
The first snow falls in the Sikkim-Himalaya at 15,000 feet, in Sep- 
tember, and does not melt always. In Sikkim the snow-line descends 
in October, in Thibet not till December; in the drier northern parts, 
it again melts up to 17,000 feet. In Thibet, as far north as Kiong-lah, 
it also often falls in the end of August and September every year, and 
melts again to 19,000 feet. As the rains are not over till October, the 
sporadic falls are numerous, and quite disguise the perpetual snow. 
You have well appreciated the several complicated phenomena of 
precipitation, evaporation, solar and terrestrial radiation. These all 
act differently, both as to amount and duration, and affect different 
times of the year, north and south of the snowy belt. Still, these 
effects are progressively greater, in going from the snows of the 
Himalaya to those of Thibet. Comparing Sikkim with the north- 
western Himalaya, I should say that the snow-line is lower in Sikkim, 
because far more falls, and the sky is more cloudy. With regard to 
the mountain axis in Asia, I do not doubt it is the Himalaya, i. e., the 
mountain mass between the Yarou and plains of Bengal. ‘The line 
of mean greatest elevation is probably 18,000 feet: it is north of the 
snowy Himalaya, and zigzag. Proportionally very little of the snowy 
Himalaya rises above 18,000 feet ; and the 300 feet of that which is 
exposed to view being always snowed, and always projected to the eye 
in a straight line, the delusive effect is that of a mountain-chain, on this 
side the main axis and water-shed. 
. I am here joined by my old friend and schoolfellow Dr. Thomson, 
of the Thibet mission ; aman of great enthusiasm, and of the highest 
scientific attainments. He had, independently, adopted the same view 
