STRATIGRAPHICAL FEATURES. 75 



8. Jurassic deposits ; Spiti shales (/?). 



Probably the widest known amongst the Himalayan formations 

 are the beds out of which the numerous and well-preserved Jurassic 

 fossils have been collected, not only by geologists and European 

 travellers, but by natives both of Tibet and India. From ancient 

 times a trade in Jurassic Ammonites has existed; great quantities of 

 these fossils are brought every year to India, chiefly to the holy 

 places of Hindu pilgrimage, and sold as relics to Hindu worshippers. 

 Long before the localities from whence these fossils came were 

 known to geologists, some of the remains were described and figur- 

 ed) 1 . But not till later on, when the brothers Strachey explored the 

 higher Himalayas, did the Jurassic deposits become known. After- 

 wards the visits to Spiti by Theobald, and the explorations by Sto- 

 liczka, resulted in a closer study of the Jurassic formations. Stoliczka 

 comprised the whole of these deposits under the name of the " Spiti " 

 shales, and as this formation is remarkably constant in lithological 

 character, over a very large area of the Central Himalayas, the name 

 is understood to define the entire thickness of Jurassic deposits. 



The system consists chiefly of shales and is well defined between 

 the liassic limestones (16) and the greenish sandstones (Gieumal 

 sandstone) of the cretaceous system. 



Apparently the Spiti shales rest perfectly conformably on the 

 beds with liassic fossils, and the only evidence of a break in the 

 continuity of the formations is the complete and absolute change of 

 lithological character as one passes from the earthy limestone of the 

 lias to the dark crumbling Spiti shales. Additional evidence in 

 favour of the supposition that there exists a break between the lias 

 and Jurassic deposits of the Himalayas is afforded by the fact that a 

 sudden change of fauna sets in with the Spiti shales. On beds with 

 liassic forms rest, as far as we know at present, strata which contain 

 organic remains of middle and upper Jurassic types. 



The upper boundary seems less sharply defined ; there the shale 



1 Trans. As. Soc. Beng.,'Pt. II, XVIII. 



( 75 ) 



