68 



GRIESBACH : GEOLOGY OF THE CENTRAL HIMALAYAS. 



Trias. 



lower trias through a series of strata which I might call passage 

 deposits, which contain a fauna exhibiting strong affinities both with 

 permian and triassic forms. This is the Otoceras horizon. 



The strata of the triassic system take perhaps the largest share in 



the mountain structure of the Central Hima- 

 layas. The greater part of the Northern Range 

 of the Central Himalayas, in fact nearly the whole of the watershed 

 range between Hundes and the Bh6t Mahals of Garhwal and Kumaun, 

 is formed of triassic rocks. 



From the Nepal frontier to Spiti, an enomous development of 

 triassic limestone, dolomite and shales rests conformably on the 

 Productus shales (9) which pass upwards into the lower trias, and to- 

 gether with these shales the trias forms a closely connected structural 

 system. The distribution of this complex of strata follows closely that 

 of the palaeozoic group ; frequently the members of the triassic system 

 form long and narrow strips inclosed in synclinals of carboniferous 

 rocks, a structure which is especially clearly seen in the Bhot Mahals 

 of Kumaun, where these synclinals are often remarkably narrow 

 troughs (see pis. 15 and 16). The upper trias, with rhsetic above, 

 generally forms precipitous scarps towards the south, often quite in- 

 accessible. 



From afar off the trias and rhaetics may be distinguished from 

 other formations by the yellow ochre colour into which they weather, 

 which strongly contrasts with the dark tints of the lower palaeozoic 

 and red and white colours of the carboniferous beds. 



The total thickness of the entire series is about 4,000 feet in the 



Niti sections, but probably exceeds that figure in 

 the area further eastwards, where the upper trias 

 and rhaetic deposits swell out considerably. 



In the following pages I have given the main divisions into which 



the trias of the Central Himalayas may be divided, 



and I have in that list adopted the numbers for 



the various divisions, which are used in my figured sections. With 



few exceptions the various horizons of the trias may be followed up 



( 68 ) 



Thickness. 



Divisions. 



