MIKIR HILLS. 75 



geologist, and occasionally the smaller ones shew a few yards of 

 rock in situ. 



The great mass of the north Mikir hills is composed of gneiss, 

 and the ranges are higher and steeper than those of the southern 

 hills. The jungle is almost as thick, however, on the northern 

 hills, but they present a fair number of rock-exposures. 



Several peaks in the north Mikir hills reach 4,000 feet in height, 

 while in the south Mikirs only one range touches 1,500 feet. 



General Geology. 



All round the foot of the north Mikir hills, sedimentary rocke 

 overlie, and abut against, the gneiss. These younger rocks stretch 

 away, southwards, over the south Mikir and north Cachar hills, and 

 eastwards, across the Dhansiri valley into the Naga hills. 



They were evidently deposited on the ancient surface of the gneiss, 

 which, being naturally uneven, has frequently given the beds imme- 

 diately overlying it a gently undulating dip, but the general lie of the 

 beds is horizontal. 



Very few of the sedimentary rocks contain fossils, but there is 

 fortunately a fairly constant band of nodular, earthy limestone, full 

 of nummulites, which is always found at or near the junction of the 

 sedimentary rocks with the gneiss. This band supplies most of the 

 evidence as to the age of the younger beds. 



At several places decomposed trap and some doubtful beds of 

 small extent intervene between the gneiss and the limestone, pro- 

 bably representing the cretaceous; but the mass of the sedimentary 

 rocks in the Mikir hills is undoubtedly of tertiary age. The chief 

 divisions with their probable approximate ages and thicknesses are 



as follows : — 



Alluvial Deposits. 



. feet. 

 Soft mottled clays, sandy soil and loose gravels . 100 



Tertiary. 



I. Pliocene . Soft yellow sandstones, locally and superficially 1,000 

 highly ferruginous : with silicified wood, rare 



( 75 ) 



