6 MEDLICOTT, SHILLONG PLATEAU. 



accumulation of its deposits at any one time. These Madtopur deposits 

 cannot be considered as belonging to tbe present delta, but probably 

 (in my opinion) to one which has been extensively destroyed throughout 

 its upper area by the action of the rivers that had formed it,"^ and owing 

 to an increase in the fall of these rivers beyond the limiting angle of 

 delta-formation, or rather of fiuviatile alluvial deposition. 



There is another natural agency by which it might be possible to 

 account for features of this kind without an appeal to crust-movements. 

 If one could imagine the very extensive destruction of the lower portion of 

 a delta by oceanic violence, the rivers would then find a free discharge 

 at a point so much higher up that, if the whole area of the delta had 

 attained the limit of slope due to its farthest advance seawards, a 

 certain amount of erosion must take place. To one who has seen 

 a great delta, any conceivable operation of this natural agency becomes 

 utterly inadequate for an appreciable result of the kind required : 

 the amount of increased fall in the river course required for the produc- 

 tion of the features now under notice would be too great to be accounted 

 for by any destruction of the lower delta from superficial causes, such 

 as an unusual violence of the sea. 



We are thus compelled to introduce changes of level ; and a little 

 further consideration shows that there must have been depression of the 

 lower region of that delta of which the Madhopur area is a remnant. 

 An elevation of the upper area only of the river-basin, although it 

 would increase the fall and thus entail the removal of previous deposits 

 within the area affected, would cause no such destruction of the lower 

 region of the delta, but on the contrary its rapid augmentation. An ele- 

 vation having its limit near the outer margin of the delta would, by 



* The whole question of how far the " old alluvium" may or may not be a marine or 

 estuary deposit, and therefore raised into its present position, is still open. It would be 

 too tedious to discuss it here, even were I prepared to make the attempt. I assume the 

 side upon which there seems to me a balance of evidence. 



( 156 ) 



