;6 SMITH : GEOLOGV OF MIKIR HILLS IN ASSAM. 



calcareous bands, and local conglomerates at feet 

 the base. Passing down into 



2. Miocene and Finely laminated grey clay-shales, with hard, 800 



Oligocene. concretionsry, calcareous bands, rare shell- 

 beds, and thin coal-seams. Resting with 

 apparent conformity upon 



3. Eocene . . Nodular, earthy limestone, highly nummulifer- 300 



ous, with associated unfossiliferous sandstones. 



Secondary. 



Cretaceous . Doubtful coal-bearing shales, overlying white 50 



chalk-like argillaceous bed, associated with 

 decomposed, mottled, earthy trap. 



Massive Gneiss. 

 Age unknown. 



It will be convenient to treat the different divisions in detail, before 

 dealing with the general arrangement of the beds. 



Crystalline Rocks. 



Nearly the whole mass of the north Mikir hills appears to be 

 composed of massive gneiss, or foliated granite. The rock varies in 

 texture from a coarse-grained, porphyritic, slightly foliated granite, 

 to fine-grained strongly banded gneiss. The colour frequently 

 changes, from black and brownish-grey, through intermediate tints, 

 to salmon-pink; but the composition alters only very slightly. 

 There is one interesting occurrence at Miji of foliated charnockite — 

 hypersthene-bearing gneiss — interbanded with the ordinary gneiss 

 of the Mikir hills. It is similar in all respects to the Madras hypers- 

 thene bearing rocks. I only met with one or two layers of the 

 charnockite, and the exposures are somewhat obscured, but it occurs 

 intimately interbanded along the foliation strike of the gneiss, though 

 the two rocks are quite distinct and do not pass into one another 

 gradually. The bands of charnockite are only 20 to 30 feet in 

 thickness. 



In the south Mikir hills only two small exposures of gneiss occur : 

 one in the peak of Longloi hill, and the other two miles south of 

 ( 76 ) 



