l6o GRIESBACH : GEOLOGY OF THE CENTRAL HIMALAYAS. 



morphic rocks of the vaikritas into it so gradual, that it would be 

 next to impossible to map exactly where one system begins and the 

 other ends. In addition to this difficulty there is a purely physical 

 one * as the junction of the two systems lies mostly in stupendous 

 elevations it is either generally obscured by masses of snow and 

 glaciers, or else by enormous cones of debris shot out by the numerous 

 glacier-filled ravines. The boundary line in the Dharma area is 

 therefore more or less diagramatic ; it is based on two actual sections, 

 in some places on observations made at considerable distances with 

 the aid of a telescope, and for the rest on conjecture. The upper 

 boundary, however, has been actually observed, and is generally as 

 accurate as such boundary lines can be The upper limit of the 

 haimanta system is definitely determined by an almost uniform belt 

 of bright-red and light-green quartz shales (3) ; they are the same as 

 observed in the Niti and Milam sections, and they form everywhere 

 the base of the lower silurian system. The belt of the haimantas is 

 roughly speaking from four to six miles broad, and I followed it from 

 the Milam valley in a south-easterly direction as far as the Nepil 

 frontier, a distance of over fifty miles. Within this belt it includes 

 some of the highest points of the Central Himalayas and numerous 

 heights of over 20,000 feet between which many of the largest glaciers 

 of this part of the Himalayas rise. 



I found the strike of the strata composing the system of nearly 



uniform north-west to south-east direction but 



Thickness. 



with very varying dip. Without making very 

 close studies of the various divisions of the system, it would be im- 

 possible to arrive at a correct estimate of its thickness, as within the 

 belt, fold on fold, with many minor dislocations may be seen which all 

 more or less have the same general strike of the belt. But I do not 

 think that on the whole I would be justified in believing the haimantas 

 of this area to be of very much greater thickness than the same 

 system is in the Niti or Bisahir sections. Some of the lowest semi- 

 metamorphic beds are certainly wanting in the Niti sections, and if I 

 estimate the thickness of the haimantas of the latter as 4,000 feet 

 ( 160 ) 



