58 GEOLOGY AND MINERAL RESOURCES OF SIKHM. 



Rungeet, of the Tista, and of their chief tributaries are generally not 

 less than 5,000 feet in depth. They are rather open towards the top, 

 but usually attain a steep gorge-like character as we approach the 

 beds of the rivers. As a consequence of this, and also of the com- 

 parative insalubrity of the lower portion of the valleys, all the monas- 

 teries and principal villages are situated at an elevation ranging from 

 4,000 to 6,000 feet. 



The snowcapped jagged ridges in the northern portion of the 

 country send down glaciers* which at present usually come down to 

 about 13,500 feet; those from the Kanchanjinga appear to descend 

 about a thousand feet lower. The perpetual snow line in Sikhim 

 may be approximately put down at 16,000 feet, so that the glaciers 

 descend 3,500 to 2,500 feet below that line. Formerly they used 

 to descend much lower than at present. Lachung, for instance, of 

 which the elevation is 8,790 feet, stands at the foot of an immense 

 terminal moraine. The Bidangcho lake, on the road between Grna- 

 tong and Jalep pass, at an elevation of 12,700 feet, is dammed at the 

 southern end by a bank of boulders which are distinctly of glacial 

 origin. Moraines occiir also about Thaugme in the Pragchu valley, 

 north of Jongri, at an elevation of about 13,000 feet. The retreat 

 of the glaciei's backwards towards their gathering ground or the 

 neve in these cases has been recent, and the ancient moraines witness- 

 ing their advance are still in situ. But the excessive rainfall of 

 Sikhim, amounting annually to probably no less than 200 inches, 

 makes the removal and re-arrangement of the glacial boulders a 

 question of very short time ; and once brought within the action of the 

 torrential streams, the boulders soon lose all traces of their glacial 

 origin. The peculiar configuration of the hills passed over by gla- 

 ciers is also soon lost owing to pluvial denudation. The glacial 

 valleys, as for instance the Pragchu, the Lachen, and the Lachung 

 valleys, are open and ^^_x shaped ; and this shape is one of the most 

 reliable evidences of their origin. But after the retreat of the gla- 

 ciers, the streams taking their place cut the valleys down deeply 

 into V-shaped gorges, and the striking distinction between glacier and 

 river valleys is soon effaced. Thus owing to the excessive rainfall, 

 traces of past glacial action are liable to extinction in Sikhim ; and it 

 is impossible to tell how far the glaciers extended in comparatively 

 remote times. The lowest height of glacial extension, for which I 

 found unmistakeable evidence, is that of Lachung (8,790 feet). Below 

 Lachung also down to a height of about 7,000 feet, the valley is open 

 and has a glacial look about it. 



* The writer has described some of the Sikkim glaciers visited by him in a paper containiDg 

 extracts from the Journal of a trip to the glaciers of the Kabru, Pandim, &c. published in the 

 " Becords of the Geological Survey of India," Vol. XilV, pt. 1. 



