52 GEOLOGICAL NOTES ON ASSA^F, 



growth which a Delta must possess : the river has laid a deposit flush 

 with its flood waters^ as regulated by a fixed level of discharge below ; 

 improvement must begin from below by the raising of that fixed 

 level. The question I have asked is, how that level comes to be so low 

 as it is. As evidence of how these quasi-deltaic conditions obtain — ^how 

 completely this stationary point of formation has been attained — I may 

 notice a remarkable feature of the Deehing. This large stream drains 

 the south-east terminal corner of the valley, as the Bramahpootra 

 proper does that on the north-east. After leaving the gorge of the hills, 

 it flows for several miles over a zone of hJiahw, the flat slope formed by 

 the coarser torrented debris. On about the middle of this slope, the 

 river being still a strong torrent, it divides into two approximately equal 

 streams ; one flows tolerably direct to the Bramahpootra above Suddya, 

 the other flows along the. base of the southern hills through the rocky 

 gorge of the Tippum range at Jyepoor and joins the Bramahpootra more 

 than a hundred miles below Suddya. That a river should form itself 

 into two (what in a delta are called cUstrihttanes) is necessary proof that 

 it is constructing, not destroying ; and that for many years such a bifur- 

 cation should be maintained, shows that there can be no choice of levels 

 between the tw^o courses. 



Some slight modification has to be made to the conditions described 



in the Assam Valley. There are here and there 

 Older alluvium, •, n • 



patches oi various extent that are raised a few 



inches over the highest present known flood level of the river ; the so- 

 called ridges of Tezpoor and of Bishnath are familiar localities of this 

 kind, it is the ground most sought after for tea plantations. Although 

 so little developed, these deposits are here the representatives of what has 

 been called the " older alluvium," so extensively found in the Ganges 

 Valley. It were of great importance that some definite opinion should 

 be formed regarding these recent formations, as at present great doubt 

 rests upon them, obstructing, if not vitiating, our speculations. It is still 

 ( 438 ) 



