60 GEOLOGY AND MINEEAL RESOURCES OF SIKHIM. 



mile below the glacier [of Kincliinjhow], and the water collects in 

 pools: its temperature is 110°, and in places 116°." — {Hooker, Him. 

 Journ., 1855, Vol. II, p. 140; see also Dr. Oldham, op. cit., jo. 33.) 



(ii) Geology. 



1. — The Gneissic Group. 



The rocks belonging to this group are the oldest, and constitute 

 the main body of the Himalayas. From near Kurseong, south of 

 Darjeeling, to the northern frontier of Sikhim it is uninterruptedly 

 traced over a distance of some 75 miles in a straight line ; whereas all 

 the later rocks — the submetamorphic slate group, the Damudas, and 

 the tertiaries — together cover an area in the outer Himalayas nowhere 

 more than six miles in width. 



Two forms of the gneiss are met with : — 



(a) In Southern Sikhim, ai^proximately south of the parallel of 

 Jongri and Boktola (about lat. 27° 250'), the gneiss is 

 highly micaceous and frequently passes into mica schists. 

 Both muscovite and biotite occm', the former predominat- 

 ing. Hornblende, garnet, and schorl are the chief acces- 

 sory minerals. Bauds of quartzite are common. Veins 

 of calcite occur at places, as near Lingtu by the road 

 to Gnatong. The gneiss is well foliated, and exhibits 

 strongly marked features of disturbance, in that it is much 

 folded and crumpled, especially in the extreme south 

 about Darjeeling. The prevailing strike is WNW — ESE. 

 (5) In Northern Sikhim, as north and south-west of Jongri, 

 about Lachung, &c., the gneiss is not quite so micaceous. 

 Muscovite is either rare or is entirely absent. Schorl and 

 hornblende are the chief accessory minerals. Intrusive 

 granitic rocks occur as dykes and sheets; in some of them 

 muscovite is well developed. 



The noi'thern gneiss agrees in some of its petrological characters 

 witli the central gneiss of Stoliczka. As the southern gneiss, how- 

 ever, was unintei'ruptedly traced into it, and as no phj'sical break 

 •was perceptible anywhere, they are very likely of the same age. 

 Mr. Medlicott takes the same view in the " Manual of Indian 

 Geology."* 



The relation between the gneissic group and the next group (the 

 Dalings), which includes submetamorphic slates, phyllites, &c., is far 

 from clear. At the eastern boundary between the two groups which 

 passes by Gantok, the j^resent capital of Sikhim, the latter apparently 



• Op. cit., pp. 597— 614. 



