66 HAYDEN: GEOLOGY OF THE PROVINCES OF TSANG AND 0. 
CHAPTER X. 
SUMMARY. 
1. To the north of Sikkim and Bhutan the orographic conditions 
are apparently much more complicated than in 
Orography. j f 
the area to the north of Nepal and Kumaon. 
The northern range of the Central Himdlaya no longer exists as a 
definite unit but merges into a series of variously oriented ranges 
with intervening depressions. The Tsangpo, however, occupies a 
continuous trough from its source to the point at which it turns to 
the south and cuts its way out to the plains of Assam. On the north 
of this trough are the Tibetan ranges, named by Trelawney Saunders 
the Gangri mountains, and to the south the high range of snowy 
peaks including Everest, Kinchinjunga, Chomolhari and the other 
giants of the Himdlaya. On the north of Nepal this latter range is 
separated from the northern range of the Central Himalaya — -the 
water-parting between the Gangetic drainage and the Tsangpo — by 
an apparently continuous depression parallel to the trough of the 
Tsangpo. To the north of Sikkim and Bhutan, however, this depres- 
sion is no longer continuous, but may be represented by a series of 
broad plains and lake basins, including the Yaru plain and Kala Tso. 
2. Stratigraphically two broad zones have been recognised, viz., 
the crystalline and metamorphic to the south 
Cr"s\'Se'2one. ^^^^ Tibetan zone of fossiliferous sediments 
to the north. The former zone embraces the 
high snowy range of the Himdlaya, and is composed of granite, 
gneiss aiid a series of crystalline and metamorphic rocks, including 
pyroxene-scapolite granulite, graphitic sillimanite gneiss, crystalline 
limestone, mica schist and quartzite. These appear to represent the 
Archaean rocks of the Peninsula and Burma ; the Dharwar system 
may be represented by the Haling series of Sikkim and the meta- 
morphosed ss^diments of the Khongbu valley may be the crushed 
representatives of the Vindhyans of the Plains. 
( ) 
