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GRIESBACH : GEOLOGY OF THE CENTRAL HIMALAYAS. 



formation passes gradually into a formation of shaly greenish sand- 

 stone, which may be of lower cretaceous age. 



The so-called " Spiti shales," which are thus limited in both 

 directions, represents, as far as it is possible to say at present without 

 having compared the fossil contents, the entire middle and upper 

 Jurassic system. The lower jurassics are doubtful, 



There are several horizons of dark shales found in the Central 

 Himalayas belonging to widely separated geological systems, but 

 nevertheless it is never difficult to distinguish the Jurassic Spiti 

 shales amongst them. Stoliczka has already given an excellent des- 

 cription of this system in his rt Memoir" to which I have little to add. 

 But as I have seen the formation in the Niti area and in Hundes, 

 where the beds forming it are seldom much disturbed, I have been 

 able to distinguish at least three divisions of the system. 



In descending order follows : — 



c. Grey shales with occasional sandstone bed. 



b. Friable dark shales with concretions containing many 



fossils. 

 a* Dark splintery shales, fossils rare with brown earthy shales 

 at the base. 



a. In most sections through the Spiti shales, I observed a small 

 thickness of rusty brown earthy shales at the base of the Jurassic 

 deposits, and immediately above the liassic limestone. Stoliczka has 

 made mention of it in his Memoir (page 83). Only traces of fossils 

 have been obtained from it, mostly Belemnites, and it is possible 

 that this horizon may be found to represent part of the lowest juras- 

 sics. In the Shal-shal sections, north-east of the Niti area, this horizon 

 may be distinctly seen. 



It is overlaid by black splintery shales, occasionally micaceous^ 

 and with rust-coloured ferruginous blotches on their fractured sur- 

 faces. The shales are very friable and decompose into a clayey mass. 

 Nodules of iron-pyrites are common in this as in the higher beds of 

 the Spiti shales. Calcareous concretions are found scattered through- 

 out this horizon, and they nearly always contain some fossil, though 



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