I30 GRIESBACH : GEOLOGY OF THE CENTRAL HIMALAYAS. 



to the freshwater sandstone and gravels seen near Dongpu, which 

 I believe to be older than the Hundes ossiferous deposits. 



When I crossed into the Nukchung valley from the Sirkia stream, 

 I did so near the boundary between the Spiti shales and the cretace- 

 ous sandstones. The Nukchung valley forms a narrow trough in the 

 cretaceous rocks ; sandstones and gritty shales with hard quartzitic 

 grits, all more or less of a dirty green and brownish green colour dip 

 to north-east. But there is so much of local disturbance and faulting 

 that it would be impossible to do more than roughly estimate the 

 thickness of the entire division; it may be from 1,200 to 1,500' in 

 thickness. About a mile south of the Nabgo encamping ground, the 

 gorge narrows considerably, and I found white limestone full of 

 bivalves (Inoceramus sp.), which I take to be upper cretaceous 

 (Chikkim limestone of Stoliczka) conformably overlying the sandstones 

 below. It is here of very inconsiderable thickness, certainly not more 

 than 150 to 180', and is further on followed by some 300 to 400' of 

 a singular rock. This is a densely hard, dark red and purple silicious 

 rock, with some layers of what appears like highly altered clay shales^ 

 and talcose schists. With it appears a dark basaltic rock, and the 

 whole is greatly disturbed. But nevertheless what bedding is left is 

 seen to be conformable to the upper cretaceous limestone. Fortun- 

 ately after a long search I found some strangely contorted speci- 

 mens of Nummulites in a calcareous portion of the altered rock, which 

 I believe will be found to correspond to the Nummulitic zone described 

 by Stoliczka from the Upper Indus, altered by a post-eocene eruptive 

 rock ; the latter must be the basaltic trap which disturbs the form- 

 ation, and I believe the albite granite and syenite, which has played 

 such an extensive role amongst the \ounger rocks of the Himalayas 

 and the Perso-Afghdn ranges, may be of nearly the same period. 

 Near Nabgo encamping ground the altered Nummulitic limestone 

 associated with basaltic rocks is well seen, especially near the left 

 side of the valley and in the gorge just north of the camp. 



Between Nabgo and Dongpu the conformity which prevails 

 throughout the mesozoic and older tertiary rocks suddenly' ceases. I 



( 130 ) 



