10 WAA6EN WYNNE : GEOLOGY OF MOUNT sfKBAN. 



The reasons which led us to unite these beds with the triassie 

 formation are, first, the uneonformity above, distinctly separating them 

 from the Jurassic rocks, and also the analogies which they present with 

 a certain division of the Spiti beds : the Nerinece here first appearing in 

 the ascending section, which is also the case with regard to the ' lower 

 Tagliag^ limestone of Stoliczka, lying next above the " Para limestone," 

 to which we have relegated our lower division. 



This leads us to consider the Nerinece beds of Mount Sirban as the 

 jirobable representatives of the ' Tagling limestone^ of Spiti. 



The variations in the sections of the whole triassie group are very 

 great. We have already mentioned that the dolomites at the base of it 

 are often absent. The slaty shales, too, of the upper sub-division have 

 only been observed in one locality, although there of more than 100 feet in 

 thickness. The dolomites at the junction of the upper and lower 

 divisions are not less changeable, being sometimes thick-bedded and 

 silieious, sometimes thin-bedded and crystalline, or even replaced by 

 gray limestones. It is possible that this changeability may be in many 

 cases only apparent and be accounted for by uneonformity or overlap, 

 while the whole group may rest unconformably upon that beneath it, but 

 in the absence of conclusive evidence this is not asserted. The group 

 forms a massive covering, sheeting the north-west slopes of the mountain, 

 occupying the position assigned to the nummulitic limestone in 

 Dr. Verchere^s sketch section, and separated by a fault, which coincides 

 with the Sulhud pass or valley from the slate mountains opposite. The 

 thickness of the triassie series may be from 1,000 to 1,200 feet. 



4<. Jurassic. — To represent this series at Sirban we have only the 

 jet black shaly clay beds, well known in Himalayan Geology as " Spiti 

 shales.^' Though much reduced in thickness, they are of great impor- 

 tance as a help to rep ognise the stratigraphical relations in this country, 

 where uniform gray limestones, from the nummulitic down to the infra- 

 triassic, compose whole mountains of 10,000 feet in altitude. Still the 



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