16 MALLET: COAL-FIELDS OE THE NAGA HILLS. 



The known coal-fields of Upper Assam occur, either close to, or 



not far from, the plains, along the skirts of the 

 Crystalline rocks ap- 

 parently not largely de- Naga and Singpho hills which constitute the 

 veloped in Patkai. -n/ i • 



northern Hanks of the Patkai. Little is known 



of the geology of the interior of these hills. From the boulders and 

 pebbles brought down by the streams, however, it may be inferred 

 that the rocks north of the water-shed are, in the main, sedimentary, and 

 that ciystalline rocks (or at least the harder varieties of such), if present, 

 are not largely developed. 



Pebbles of crystalhne rocks are found in the Dihing, and it is very 

 probable that such rocks exist high up the course of that river towards the 

 snows from which it takes its rise. Crystalline rocks are known to occur 

 in the hills north-east of Sadiya, and may extend in a south-easterly 

 direction towards the head-waters of the Dihing. 



In the Dirak, a small stream which joins the Dihing about ten miles 

 below Makum, amongst the mass of sandstone pebbles, are a few small 

 fragments of gneiss and quartz-schist. There can be little doubt, however, 

 that these are merely pebbles washed out of the sedimentary rocks : the 

 ridge at the head of the Dirak is the continuation of that at Rangkatu where 

 the rocks are sedimentary and strike parallel to the ridge. Between 

 Rangatu and the plains, rocks of the same class only are met with. 



I observed no debris of the older rocks in either the Disang or the 

 Taukak, but in the SafFrai pieces of foliated and granitic gneiss, white 

 quartzite and quartz-schist (the latter containing spangles of silvery 

 mica) and hornblende rock are not uncommon, some of the lumps being 

 nearly a foot in diameter. I have never seen any conglomeritic band in 

 the newer rocks from which these could have been derived ; and such 

 conglomerate if present towards the head of the Saffrai must be 

 of very local occurrence, as no similar fragments are to be found in the 

 Taukak or Dikhu, the drainage areas of which adjoin that of the Saffrai 

 on either side. The absence of such, however, also shows that if crystalline 



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