so MALLET : COAL-FIELDS OF THE NAGA HILLS. 



tributary stream which joins it north-west of Borgong. The shale-beds 

 are grey or dark-grey, often rather clunchy, and sometimes exhibit what 

 seems to be an imperfect cleavage. The lower beds are often arenaceous, 

 and include occasional nodules of calcareous sandstone. 



In the Janji, and its tributary the Sanga jan, the shales are largely 

 developed, with the same lithology as further east. They are grey; 

 sometimes clunchy, sometimes splintery, with occasional beds of fine- 

 grained, rather hard sandstone interstratified. Pebbles and boulders of 

 sandstone of the Naogaon (Disang) type are washed down from the 

 ridge south of the Sanga jan. 



The thickness of the Disang rocks is very considerable ; probably 

 some thousands of feet. They appear to contain no coal whatever, and 

 differ lithologically from the coal-measures in other respects also. The 

 Disang shales, although interbanded with sandstone, are still, in the 

 main, shales throughout, while in the coal-measures, shale, sandstone 

 and coal occur in frequent alternations. The more characteristic coal- 

 measure shales, again, are more tenacious, less clunchy or splintery 

 than most of those in the Disang beds, and they pass into carbonaceous 

 varieties. The coal-measures contain nodules of clay ironstone also, 

 which I have not observed in the older strata. 



The distinctness of this large group of strata from the coal-measures 

 being thus fairly established on petrological 

 grounds, it can certainly be inferred that they are 

 the older of the two — the coal rocks being undoubtedly covered by the 

 Tipam sandstone. I have, however, little or no stratigraphical evidence 

 in proof of this inferred relation. The group has been principally 

 observed along the main fault, in contact with the Tipdm sandstone, the 

 ground to the south not having been visited. Where seen contiguous 

 with the coal-measures, the junction is also presumably a faulted one. 



This position, beneath rocks the most probable age of which is 

 nummulitic, suggests the possibility that the Disang beds may be 



( 288 ) 



