CRYSTALLINE ROCKS. 77 



Bokula Ghat. The general foliation strike of the gneiss is very 

 inconstant, but the dip is usually either vertical or inclined at a high 

 angle. The strike is continually changing, but the most frequently 

 observed direction of foliation was east and west. 



Occasional veins of quartz are seen in the gneiss. Near the 

 junction of the Jamuna and Langapoo nalas, one of these takes the 

 form of quartzose schist, becoming in places garnetiferous and mica- 

 ceous. 



Under the microscope, the various specimens of gneiss appear 

 very similar. They are nearly all fresh, uncrushed rocks, one or two 

 only showing some signs of crushing. They are composed of quartz ; 

 plagioclase felspar, shewing frequent lamellar intergrowths ; rare 

 orthoclase ; brown biotite and green hornblende; grains of mag- 

 netite, sometimes passing into haematite, and granules of apatite, 

 zircon, and occasionally brown rutile. One or two bright yellow- 

 green crystals in one section are probably epidote. Graphic and 

 micro-pegmatitic structure is frequently seen amongst the quartz and 

 plagioclase. 



The charnockite under the microscope is a coarse-grained fresh 

 looking rock, shewing little crushing. The groundmass is chiefly com- 

 posed of quartz grains, traversed by thin lines of inclusions, and 

 slightly decomposed plagioclase felspar, with much hypersthene — 

 pleochroic light-green to pink — scattered through it. Brown biotite 

 is common, and many grains of magnetite occur, some of which are 

 associated with a dark-green isotropic mineral, apparently a spinel 

 (hercynite). Small granules of apatite and zircon are also seen. 



There seems to be a remarkable absence of trap-dykes in the 

 gneissic area; in fact, I have only seen one un- 



Trap-Dykes. 



doubted dyke. A few exposures of soft, green 

 hydrated trap occur in some of the rivers, but they do not appear to 

 descend to any depth. When at Pangso, on the Nambor river, I was 

 taken by the natives to a reported thick seam of coal, in the hills 

 between the Nambor and Doigrung rivers. When I reached the spot, 



( 77 ) 



