OLDHAM : GEOLOGY OF MANTPUR AND NAGA HILLS. 23 



the alluvium lying immediately to the east of what is now the barrier, 

 and was formerly the water-shed of the Jamuna, was raised to its level, 

 the first flood breaking through the banks of any of the affluents of 

 the Dunseri naturally found an exit through the gap, and so struck out 

 a new course for itself which it retained, and by a continuation of the 

 same process, combined with an actual wearing away of the barrier, 

 gathered to itself the waters of the other streams flowing down in its 

 neighbourhood, and so part of the original drainage of the Jamuna, of 

 which it had been robbed by the Dunseri, now flows once more in its 

 original course. The large area of the Dunseri alluvium drained by the 

 Jamuna is due partly to the well-known law by which alluvial plains 

 slope from the banks of the depositing river, and partly to the cutti no- 

 down of the barrier, thus enabling the streams to cut back their head- 

 waters and divert to themselves more and more of the drainage of the 

 Dunseri ; this latter has, however, not yet occurred to any great extent, 

 as may be seen by the very small depth of the channels in which the 

 streams flow, and it is owing to this evidently very slight erosion of the 

 barrier that I attribute a recent date to the escape of the present stream 

 of the Jamuna in that direction, and it is not improbable that the subsi- 

 dence which has caused this change in the drainage here was the same 

 as that which put an end to the conditions under which the high-level 

 deposits of the Naga hills were formed. 



49. The region under description is very poor in minerals of econo- 



niic importance, but iron, copper, gold, salt, lime, 

 and edible earth are found in small quantities. 



50. Iron is found in more than one locality in the valley of Manipur ; 



but so far as I know is confined to the swampy 

 alluvial bays, where it is found in the shape of 

 small pisolitic nodules of hydrated oxide of iron (bog iron ore) inter- 

 mixed with clayey matter. The bed in which the ore is found is never 

 at the surface, but covered with alluvium to the depth of two to five 

 feet, and is itself from three to twelve inches thick. To procure it pits 

 are dug, the barren soil above is thrown aside, and the band containing 



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