72 SMITH : GEOLOGY OF MIKIR HILLS IN ASSAM. 



river-bed is full of exactly similar pebbles, so the ridge probably 

 represents merely a sub-recent river deposit. 



Along the Jatinga valley soft clay-shales and shaley sandstones, 

 shewing much disturbance, are seen to be overlaid, in the ranges to 

 north and south, by a great thickness of massive sandstone. 



Good sections are frequent in the railway cuttings, the shaley rock 

 taking the following forms: nodular, grey clay- shales ; finely lami- 

 nated shales and shaley sandstone, with thin, micaceous layers ; blue, 

 splintery shales, with sandy beds and irregular bands of blue, mica- 

 ceous, calcareous sandstone ; dark blue-grey clay-shales, with thin 

 bands of greenish sandstone and gypsum. Occasional threads and 

 bands of lignite, up to an inch or two in thickness, occur in the 

 shales. 



Great disturbance is seen throughout, the beds dipping steeply 

 in all directions, and in several cases they are seen to be torn off 

 suddenly by small faults. 



The difficulties of making a railway over this sort of rock are 

 great. For instance, near Dumcherra a tunnel had been cut through 

 a spur along the strike of the shales. When the excavation was com- 

 plete, the slab of vertical shales over the tunnel slipped bodily down 

 into it, obliterating the tunnel, and leaving a corresponding cutting 

 over the surface of the spur. 



Several thin bands of coal occur in a tunnel to the south of 

 Kayeng, but they are only a few inches each in thickness, and of 

 no economic importance. 



Approaching Haflong the shales gradually die out and are re- 

 placed by more and more massive sandstone, showing frequent false 

 bedding and ripple-marked surfaces. 



Along the crest cf the range, to the north of the upper Jatinga 

 valley, great thicknesses of this massive sandstone are seen horizon- 

 tally bedded ; and along the Burrail range, to the south of the valley, 

 similar beds occur dipping away 2o° to 30° S. E. Haflong is situated 

 on this sandstone, which is a softish, fine-grained rock, grey-green in 



( 72 ) 



