TRANS-HIMALAYA AND TIBET 45 



horizontal alluvial deposits (with bones of rhinoceros, etc.) 

 but also by volcanic rocks, which must have risen up in the 

 form of molten lava from vents along the fractures bordering 

 the rift valley, exactly as in similar cases of such valleys in 

 Syria, Armenia, East Africa and other parts of the world. 

 Immediately on either side of this longitudinal depression or 

 groove, however, we find only much older rocks — viz. Jurassic 

 schists, granites, porphyries, etc. 



The Gartok-Indus valley appears to be of a similar nature, 

 branching off in a more north-westerly direction ; here also 

 volcanic rocks occur in the valley, lying between and at the 

 foot of high granitic walls as far as Kangmar, near the seventy- 

 eighth meridian. Although this region has not been extensively 

 explored, yet hot springs have been noticed in several places 

 along the northern side of this rift-valley — e.g. about twenty 

 miles south-west of Gartok and also on the north side of the 

 Gye-gong-la pass on the Kanchung-gangri, etc. — and it is well 

 known (as I have already had occasion to remark) that hot 

 springs are characteristic of tectonic lines of fracture. 



The map will readily show that the Trans-Himalayan arcs, 

 at least those which are complete arcs and have escaped being 

 truncated by faults, exhibit a sharper curvature than the present 

 arc of the Himalaya taken as a whole. Now the folding of 

 the Trans-Himalayan rocks probably took place in the Upper 

 Cretaceous or the Lower Tertiary period, for Nain Singh ^ dis- 

 covered Omphalia Trottcri, Feistmantel, of Upper Cretaceous 

 (Turonian) age on the shores of the Nam-tso or Tengri-nor, 

 on the northern border of the Trans-Himalayan zone. It has 

 been established that at this period the Punjab Himalaya was 

 not in existence (its formation was subsequent to that of the 

 Nepal Himalaya) and that even down to the Upper Eocene the 

 sea still existed in that region. It must have been a steadily 

 sinking area to allow of the great accumulation of nummulitic 

 limestone, which has now been raised to the height of 18,500 ft, 

 in the Zanskar range, on the peaks above the Singhgi-la.^ This 

 geosyncline of the Punjab Himalayan area would at the time 

 of the folding of the Trans-Himalayan arcs have stood in 

 a similar relation to them as the Mesopotamian and Persian 

 Gulf geosyncline stands at the present day to the outer Iranian 



' Records Geol. Survey of hidia, x. p. 21. 



* T. D. La Touche, Records Geol. Survey of India, 1888, xxi. p. 160. 



