438 CLOUD-BELTS ON MOUNTAIN SLOPES. 



with astonishing rapidity upon mountains, so that it is 

 seldom possible to judge how long the atmosphere will 

 continue clear. 



The cloud-caps on mountains present several features 

 worthy of attention. The most common form of these 

 enshrouds the mountain tops with a screen of vapour, 

 impenetrable to the eye. These clouds may rest 

 immovably upon the higher slopes, even for days, 

 when the atmosphere a few thousand feet beneath 

 is quite clear, and the sun shining brightly, showing 

 how thoroughly local are these cloud-caps, which 

 are doubtless caused by the condensation of vapour 

 caused by the cold of these great elevations. At 

 other times a belt of smoke-like mist lies all along 

 the breasts of the hills, leaving the summits per- 

 fectly clear ; this form of cloud bank is very com- 

 mon on the Himalayas, and is probably due to the 

 cloud meeting with an opposing current of air, at its upper 

 limits, which prevents its ascending beyond that point. 



In the rare instances where there are roads or lines of 

 mountain railway, it is often possible by this means to pass 

 up or down completely through the cloud-belt, into the 

 clear atmosphere of the higher or the lower levels. We 

 have seen a remarkable instance of this while descending 

 the railway from Darjeeling, in the Sikkim Himala- 

 yas. * At Ghoom, 7407 feet over sea-level, on the crest of 

 the ridge, the atmosphere was clear and frosty, descending 

 to "Sonada," 6390 feet, the train entered the cloud-belt. 

 At Toong, 5470 feet, the mist became very dense, and 

 the wind fell to a dead calm. At Kursong, 4732 feet, 

 no object was visible at over 50 yards. A little below 

 this the sky began to clear; and at Mahanaddy, 4120 



* Jan. 23rd, 1893. Details extracted from the Author's notebooks. 



