126 GR1ESBACH: GEOLOGY OF THE CENTRAL HIMALAYAS. 



The Sherik river has deeply eroded through the great sheets of 

 liassic limestone, and reached the upper rhaetic dolomites and lime- 

 stones. A most picturesque gorge (fig 19) some four miles above 

 the junction of the Sherik stream with the Shanki river shows the 

 sequence of the upper rhaetic and liassic strata, though the whole 

 is greatly shattered and disturbed. The white sections of Megalodon 

 sp. in the dark dolomites, and higher up the Lithodendron weathered 

 out in the dark rock clearly indicate the horizons. The liassic system 

 is defined by its stratigraphical position between the upper rhaetic beds 

 with Brachiopods, and the fossiliferous Spiti shales. The lower beds 

 of the lias consist of light-coloured grey limestones, weathering a rusty 

 sienna colour ; near the upper beds, a zone of dark calcareous shales 

 with oolitic structure has yielded some fossils, chiefly Ammonites, and 

 many Belemnites. This bed I have also met with in other sections, as 

 for instance near the top of the Niti pass, and near Bara Hoti east of 

 the Silakank. It is in all sections overlaid by a gritty grey limestone 

 or calcareous sandstone with many fossils, chiefly Bivalves. The 

 contact bed between the upper lias and the Spiti shales is a coarse 

 conglomerate, chiefly made up of fragments of triassic and rhaetic 

 limestones. 



The section through the lias is therefore in descending order : 

 overlaid by Spiti shales. 



3. Gervillia limestone. 



2. Dark calcareous shales, oolitic structure, fossils ; 



I. Flaggy limestone, light grey in colour; great thickness ; 



The Spiti shales form low undulating ground north-east of the 



Spiti shales north steeply inclined limestones of the lias, and may 

 of Niu pass. ^ e recognized from afar off by the dark colour 



of the rounded outlines of the hills. The contact rock I found to be 

 a coarse conglomerate formed of the limestones of the underlying 

 beds. On it followed about 1,350 feet of Spiti shales. The lowest 

 portion of the latter is very ferruginous and yielded no fossils. 

 Higher up the shales contained many nodules, nearly all of which 

 enclosed fossils, chiefly Ammonites of middle Jurassic types. Above 

 this horizon, Ammonites become scarcer, but the nodules furnished 



( 126 ) 



