2 OLDHAM : GEOLOGY OF MANIPUK AND NAGA HILLS. 



incomplete in itself, has, taken in conjunction with and explained by my 

 own work during the past season, enabled me to colour in a large area 

 I should otherwise have been compelled to leave blank. 



3. In the following description I shall proceed in order of the various 



„,,,,, . ,. „ formations seen, commencing- with the oldest: as 

 Method of description ; => ' 



adopted. ^he method of description by localities, while more 



convenient in the case of traverses would be very inconvenient when 

 describing the connecting surveys I was able to make. 



4. I will therefore commence with a series of slates, sandstones and 



quartzites, which occupies the greater part of the 

 Older series* 



area visited, and which I will provisionally call the 



* older series/ deferring for the present the consideration of its age or 



title to a separate designation. 



5. These beds were met with for the first time shortly after passing 



the Mukru river, on the road from Cachar to 

 General description. . _ . 



Mampur, where, two miles alter crossing the river, 



the steady north- 10°-east strike of the upper tertiaries suddenly ceased, 

 and rocks, not at first very distinctly different in appearance, came in 

 with a dip constantly changing in direction and amount, but settling 

 down on the crest of the Kala Naga ridge to a south-easterly dip, which 

 near the crest is 60° but as the road sinks down into the Barak valley 

 is seen, while continuing steady in direction, to gradually decrease till in 

 the bed of the Barak the strata are quite horizontal ; this horizontality 

 continues up the eastern slope of the Barak valley for some 1,000 feet, and 

 here the series contains some beds of almost pure pipeclay. Beyond 

 the village of Ballung (Bolongdoay) the dip again becomes south-east 

 at 20°, and from here to the bed of the Irang the dip is constant to 

 either south-east or east- 10°- south, and generally about 20°. In the 

 Irang the rocks are once more horizontal and continue so about half- 

 way up the eastern slopes, whence they have a low dip to the west, all 

 the way up to the crest of the ridge. After leaving the valley of 

 Mapum the strike, though at first north and south, soon turns rouud to 

 north-east and south-west, which, with local irregularities, continues with 

 ( M8 ) 



