COUNTRY BETWEEN KOTAH DCN AND NEPAL. IOI 



beds of old basic lava-flows ; for they are not only regularly interstrati- 

 fied with slates and quartzites of sedimentary origin, but they are also 

 frequently charged thickly with amygdules of chalcedony and other 

 secondary minerals, which fill up what were vesicles in the rock at 

 the time of its birth. These filled up vesicles proclaim at once that 

 the rock was exposed at the surface in a molten condition, that it 

 was a flow or lava sheet and not a dyke rock. Furthermore, these 

 supposed intrusive traps have not baked, hardened, or metamorphos- 

 ed the Nahans in any degree whatever. On the contrary, these sand- 

 stones at Amratpur in the vicinity of the trap are rather soft and 

 friable, and exhibit no sign of having been subjected to such volcanic 

 heat as must have been developed at the time those vast beds of lava 

 welled up from beneath the crust, Still further, the rock next to the 

 Nahans at Amratpur and Amia village is not trap mainly, but a good 

 strong granite of normal character and white colour : that is to say, a 

 deep-seated rock, which could not have been formed except at great 

 depths under conditions of pressure and very elevated temperature, 

 and in the presence of water or water vapour — conditions which must 

 have left traces of still more intense metamorphism in the rocks 

 among which it was intruded than that due to lava. Again, the 

 quartzites and purple slates interbedded with the traps represent 

 contemporary sediments that were forming at the time the lava was 

 formed ; and the signs of age stamped on them, that is to say, the 

 pyro-metamorphism and dynamo-metamorphism which have affected 

 them, illustrate the least degree of metamorphism we should expect 

 also in the Nahans, were the latter older than the traps. 



It is clear, then, that the Nahans are a younger set of rocks, sepa- 

 rated from an older set of bedded volcanic and plutonic rocks which 

 happened to be exposed in this locality during the time when the 

 main-boundary fault was in progress of formation. As such, they 

 are as distinct from them as from any other Himalayan rocks else- 

 where in contact with them at the main boundary. 



There are many other points of interest in these Pre-Tertiary ig- 

 neous rocks, as we trace them along the course of the Gola R. up 



( "59 ) 



