%1 OLDHAM: GEOLOGY OF MANIPUR AND NAGA HILLS. 



the Kubo valley and the alluvial plains of the Ningti ; it is evident, too, 

 that Griffiths, in his tour from Assam to Bhamo, passed through several 

 similar valleys, though he does not take any particular notice of the 

 fact. The Kubo valley may not impossibly be a 

 filled-up lake, for not only are there pretty dis- 

 tinct traces of an elevated terrace at its northern end, but in one of the 

 small streams, not far from the northern limit of the alluvium, I dis- 

 covered a bed of fine clay, almost pipeclay, which could hardly have been 

 deposited by a stream flowing over an alluvial plain. 



48. The alluvium of the Dunseri valley, though it has probably 



shut out for ever the possibility of tracing the 

 Dunseri valley. . 



connection between the cretaceous and nummu- 



litic rocks of the hills to the west and the coal-bearing rocks to the 



north-east, is not without interest of its own. That the valley of the 



Dunseri is a longitudinal valley, which has extended itself along not 



merely the strike of the rocks but along the line of weakness separating 



the two contrasting areas of the Mikir and Naga hills, there can be but 



little doubt, for the large open valleys through which the Jamuna and 



the now insignificant stream of the Langpher flow, carrying part of the 



drainage from the Dunseri alluvium into the Diyung, could not have 



been formed except by rivers draining from a much larger area to 



the east than they now do. But after the Dunseri had thus diverted 



the drainage from the east into its own channel, a subsidence of the 



land took place, causing the formation of the Dunseri alluvium. Though 



this subsidence was probably divided into several stages, some of them 



perhaps dating from pliocene times, we have indications that the last 



stage of all must have been of geologically recent date, for some eight 



miles below Mohendijua the Jamuna river falls over a barrier of gneiss ; 



now until by subsidence of the land the alluvium of the Dunseri had 



been raised to the level of this barrier, all the drainage that now falls into 



the Jamuna to the east of or above it must have flowed into the Dunseri, 



but a river depositing alluvium always raises its banks and the surface 



of its waters above the level of the surrounding country so that after 



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