$4 SMITH : GEOLOGY OF MIKIR HILLS IN ASSAM. 



there is perfect parallelism of stratification and apparent conformity, 

 but at the same time a complete change of facies comes in. Massive 

 limestones, full of foraminifera, are overlaid immediately by finely 

 laminated, grey clay-shales, with usually no trace of fossils. Besides 

 this, the shales rest on nummulitic sandstone beds to the south and 

 limestone to the north ; and the nummulitic band decreases in size 

 and thickness from south to north, being eventually overlapped by 

 the shale series. This all points to the fact that there is some uncon- 

 formity between the two, but the intervening disturbance has been 

 so slight that the parallelism of their strata remains perfect. 



The younger tertiary beds remain very constant throughout the 

 Mikir hills. They consist of a lower series of grey clay-shales, with 

 frequent calcareous, lenticular concretions and bands, occasional 

 thin bands of lignitic coal, and rare shell beds, passing upwards, 

 through local bands of conglomerate near the junction, into an 

 upper sandstone series, with rare calcareous bands, and much silici- 

 fied wood at the base. The two series can be traced southwards, 

 across the Lumding plain, to the corresponding beds of the North 

 Cachar hills. 



Lower Siwaliks — Shale-series. 



The grey clay-shales are probably the reported coal-bearing rock 

 of the Mikir hills. Thin veins of brownish coal do occur in them, 

 but none that I have seen exceed 18 inches in thickness, and the 

 coal is generally intercalated with shale. 



Exposures of the shale-series are only met with in the deeper nala 

 beds. They present exactly the same appearance throughout the 

 whole of the Mikir hills, a few subordinate bands alone causing any 

 alteration in them. 



In the Meyongdisa valley some fair exposures occur. Near the 

 junction of the Megik nala with the Meyong- 



Meyongdisa river. ..... . 



disa the nummulitic beds are overlaid horizontal- 

 ly by finely-bedded, grey clay-shales, with sandy bands, and one or 

 two strings of lignitic coal an inch or two in thickness. Further up 

 ( 84 ) 



