8 MEDLICOTT^ SHILLONG PLAfEAU. 



a portion of the present deltaic area, especially on its eastern side, is 

 only in confirmation of other independent evidence. 



Along" the south base of the Shillong plateau from east to west the 

 process of alluvial formation, and the preponderating influence of the 

 Bramahpiitra, are well exhibited. In Silhet, swamps and perfectly level 

 alluvial flats stretch up to the very base of the steep rocky hills ; and the 

 rivers for a short distance have a steep fall in very shallow and variable 

 beds over the coarse debris they have themselves brought down ; they 

 very soon, however, loose all perceptible fall, becoming Mais, or tortuous, 

 anastomosing, slack-water canals — ^the condition of all the minpr water 

 channels in a delta. Westwards, in Mymensing, the general level of 

 the plains rises gradually but considerably ; swampy areas are rarer ; 

 there are locally the beginnings of undulation from pluvial denudation, 

 showing that deposition has there reached its limit for some time ; depo- 

 sition has begun to encroach upon the river-gorges ; the coarser debris 

 scarcely reaches the open country, and rock-barriers do not occur for spme 

 distance up the gorges ; the water-surface in wells in the dry weather is 

 eighteen to twenty feet below the general level of the country. It is 

 evident that the contrast I have described between the conditions of the 

 surface in Silhet and in Mymensing is due to the great accumulation of 

 detritus from the Bramahpiitra during the time when it flowed to the 

 east of the Madhopur terrace ; and it is equally evident that the recent 

 change in the course of that river is due to the elevation thus temporarily 

 produced in this eastern channel above that of available channels to the 

 west of the Madhopur terrace. It is probable that its period in this 

 western course will be of comparatively short duration j the Ganges and 

 the great Himalayan tributaries being its competitors for that ground. 



It is worthy of notice that the comparatively recent depression of 

 the eastern area of the delta, far into Silhet and Cachar, as exhibited in 

 the features of the alluvial deposits, is a continuation of the same phe- 



( 158 ) 



