OLDHAM t GEOLOGY OF MANIPUR AND NAG A HILLS. 21 



innumerable sheets of water and the low hills rising island-like from its 

 surface all suggest the simile of a lake. Had this been the past history 

 of Manipur, the present plains must either have originally formed the 

 lake bottom, or have been produced by the gradual silting up of the lake 

 and approximately mark the old water level. Major Godwin-Austen, 

 the only one of previous observers who can be said to have had any know- 

 ledge of geology, rightly rejects the former, but adopts the latter supposi- 

 tion; in which I must differ from him, for it is impossible that, during the 

 ages necessary for the gradual filling up of so large a lake, no terraces 

 should have been formed by the inevitable cutting down of the outlet • but 

 as has been mentioned no such terraces are to be seen, and consequently I 

 am obliged to reject a lacustrine origin, for at least the upper beds of 

 the Manipur alluvium. The Longtak lake, which has been appealed to as 

 evidence of past lacustrine conditions in the Manipur valley, has no bear- 

 ing on the question, as, in the absence of any information about its depth, 

 it may be due to mere inequality in the rate of deposition of the alluvium. 



46. A very marked peculiarity of the rivers flowing over the allu- 

 Peculiarities of drain- vium, and which is further proof of its rivial, 



age ' rather than lacustrine, origin, is the manner in which 



many of them flow through gaps in the ridges which rise above the plain 

 instead of round them as might have been expected ; this feature is 

 especially marked in the streams flowing into the north-west corner of the 

 valley which all pass through the ridge that runs northwards from the 

 town of Manipur. There can be but little doubt that this is due to the 

 greater deposit of alluvium in the old valley of the Tiki, having risen to 

 the level of the gaps in the ridge to the east, when the streams naturally 

 flowed through these gaps into the lower level of the alluvium of the 

 Imphal ; so, too, the Iril having raised its alluvium till it found an 

 easier outlet through a gap in the hills to the west, deserted its old 

 course to adopt the one in which it now flows. 



47. Alluvial plains surrounded by hills are not uncommon in this 

 Similar de it region. Besides that of Manipur and the small one 



in which the Kaopum thanna is situated, there are 



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