88 SMITH: GEOLOGY OF MIKIR HILLS IN ASSAM. 



Upper Siwalihs — Sandstone-series. 



Overlying the horizontal shales, which have a total thickness 

 of some Soo feet, come about 1,000 feet of sandstones, which are 

 usually horizontal also, and probably quite conformable with the 

 shales. The sandstone beds only occur capping the low south 

 Mikir hills, to the south of which they are connected with the 

 sandstones of the north Cachar hills. Two forms of rock occur 

 representing the sandstone series. Firstly, a dull-red or purple to 

 light- pink, soft, earthy sandstone, more or less ferruginous. When 

 any depth of section of this rock is exposed, the surface rock is murh 

 more ferruginous than the underlying beds. The sandstone often 

 becomes an earthy, sandy haematite superficially, and the soft rock 

 is frequently penetrated in all directions by veins of compact haema- 

 tite, up to an inch in thickness, enclosing rounded lumps of soft 

 sandy rock. 



Secondly, a coarser grained rock, usually an earthy, haematitic 

 conglomerate sometimes vesicular and resembling laterite, with 

 small quartz pebbles included in it. It generally occurs capping 

 the lower hills, representing probably the basal beds of the sand- 

 stone-series. 



The sandstone, like the greater part of the grey-shales, is 

 unfossiliferous, except in the matter of silicified wood. Lumps of 

 fossil wood, entirely silicified, but never carbonaceous, up to 4 and 

 5 feet in length, occur abundantly at the base of the sandstones, and 

 probably at the top of the shales also, but no trace of coal is met 

 with in the sandstone-series. 



Nambor Coal Beds. 



About 8 miles above the falls on the Nambor river a curious 



small patch of coal-bearing rocks occurs, mentioned previously by 



Messrs. Mallett 1 and LaTouche. I think it is an isolated patch, as 



gneissic hills certainly surround it to the west, south and east ; but , 



1 Mem. Geol. Sur., Ind., Vol. XII, Pt. 2, p. 17, footnote. 



( 88 ) 



