42 MEDLICOTTj SHILLONG PLATEAU. 



the nummulitic formation at Cherra are certainly reduced to a mere 

 shadow near the Bramahputra^ but until the true limits of the formation 

 are known, it cannot be asserted that the whole formation decreases west- 

 wards. It is in the supra-nummulitic deposits that this change is most 

 remarkable ; but we must go further east than Cherra to notice it : there 

 is an enormous thickness of upper sandstones in North Cachar that 

 can be but feebly represented at or west of Cherra ; and it is precisely 

 with the loss of these rocks that the most conspicuous results of disturb- 

 ance disappear. 



In the western region, where the magnitude and intensity of the 

 disturbing action is so much reduced, we obtain observations, probably 

 better than are to be had elsewhere, upon the form of the disturbance. 

 The facts have a two-fold interest : one, in so far as they corroborate 

 what has been said upon the agreement of the stratigraphical features 

 of this region with a well known theory of a natural sequence for these 

 complicated phenomena ; and secondly, in so far as they may supply a 

 link in that theory by suggesting a partial law for the modus operandi 

 of the process postulated by it. In the section of the Theria river there 

 is but one continuous dip to the south ; it is lowest in the bottom 

 strata, increasing steadily to the vertical in the outermost and youngest 

 (supra-nummulitic). Ip. the Bogapani, only seven miles to the west, 

 this feature is modified : the average dip is higher, but at the river^s edge 

 on both banks, the bottom nummulitic limestone and its covering sand- 

 stone, from a southerly dip of 70°, suddenly become almost horizontal; 

 the unbroken continuity of the beds in the sharp bend being well seen. 

 They continue thus for about half a mile, with a southerly slope of 3° 

 to 5° ; the sandstone becoming covered by the second band of limestone, 

 which forms low cliffs on the left bank. There is then again a sudden turn 

 down to the south ; and the section ends, all the younger strata being de- 

 nuded. It is on the Sumesari, where the section at the base of the plateau 

 is fourteen miles wide, that these flexures are well seen. They are repre- 



{ 192 ) -■ 



