GEOLOGY AND MINERAL EESOURCES OF SIKHIM. 57 



NOTES ON THE GEOLOGY AND MINERAL RESOURCES 



OF SIKHIM. 



By p. N. Bose, B.8C. (london), f.g.s., Deputy Superintendent, Geological 



Survey of India. 



(i) Physical Geography. 



SiKHiM is essentially a mountainous country without a flat piece 

 of land of any extent anywhere. The mountains I'ise in elevation 

 northward. The high serrated, snowcapped spurs and peaks culmi- 

 nating in the Kanchanjinga, which form such a characteristic and at- 

 tractive feature in the scenery of Sikhim, are found in this direction. 

 The northern portion of the country is deeply cut into steep escarp- 

 ments, and, except in the Lachen and the Lachung valleys, is not 

 populated. Southern Sikhim is lower, more open, and fairly well 

 cultivated. 



This configuration of the country is partly due to the direction 

 of the main drainage, which is southern. The Himalayas on the 

 Indian side must have sloped to the south from the earliest geo- 

 logical times when the gneiss which constitutes their main body was 

 elevated. For all the later rocks — the submetamorphic slate group, 

 the coal-bearing Damudas and the tertiaries — which fringe the outer 

 Himalaya are evidently formed of detritus carried from the north. 



The physical configuration of Sikhim is also partly due to geolo- 

 gical structure. The northern, eastern and western portions of the 

 country are constituted of hard massive gneissose rocks capable of 

 resisting denudation to a considerable extent. The central and south- 

 ern portion, on the other hand, is chiefly formed of comparatively 

 soft, thin, slaty and half-schistose rocks which are denuded with 

 facility, and it is this area which is the least elevated and the best 

 populated in Sikhim. 



The trend of the mountain system, viewed as a whole and from 

 a distance, is in a general eas^t-west direction. Tlie chief ridges in 

 Sikkim, however, run in a more or less north-south direction, as, for 

 instance, the Singalela and the Chola ridges. Another north-south 

 ridge runs through the centi'al portion of Sikhim separating the Run- 

 geet from the Tista valley; Tendong (8,676 feet) and Moinam (10,637 

 feet) are two of its best known peaks. This north-south direction of 

 the principal ridges is due, no doubt, to the original southern slope 

 of the Himalaya. The Rungeet and the Tista which form the main 

 channels of drainage, run nearly north-south. The valleys cut by 

 these rivers and their chief feeders are very deep. The valleys of the 



