. s 4 MILMH.EMISS: PHYSICAL GEOLOGY OF SUB-HIMALAYA. 



wards the plains they gradually rise into higher ground as lower and 



harder beds set in ; and, finally, the Nahan sandstone shews beneath 



them in a normal and conformable succession. Travelling along the 



road to Kolu chaor, in the Kotri dun, from the head of the Sona N., we 



keep entirely to the sand-rock, and the only trace of the horizontal 



displacement is to be found in the curving of the strike. At the head 



of the Sona N. the latter has become east and west instead of S.E. 



and N.W.; then, after crossing the low divide into the Kotri dun, we 



find a return of the strike to S.E. and N.W., which is retained for some 



way, until near the Kotri stream when the strike becomes due north and 



south, and then a little east of north. The S-shaped trace which the 



strike thus makes is obviously of an analogous nature to the S- or 



sigma-shaped bend of a sigma-flexure. 



In a section up stream from the plains along this river, there are 



first Nahan sandstones, somewhat disturbed, 

 Kotri or Sanneh R. (37) 



near the timber depot at Sanneh (Sanai). As 



we traverse the first north and south reach of the river, we cross a 

 synclinal with axis east and west and dips of about 20° on either side, 

 increasing on the north side to 40 . The next reach, N.W. and S.E., 

 shews dips of 40 towards the east, that is, at right-angles to the pre- 

 vious dips. Again, at Mandawala parao, half a mile further up stream, 

 we have an anticlinal with axis east and west. A quarter of a mile 

 further, at Gosam parao, an E.S.E. dip of 6o° sets in and steadily con- 

 tinues decreasing in steepness to 30 as the Nahan sandstone merges 

 into the sand-rock at Sain parao. 



The river-bed has been a gorge hitherto, except near the mouth, but 



it now begins gradually to open out among the 

 Kotri dtan. , . .„ -. . . 



softer sand-rock. Several alluvial flats appear, 

 helping to give the low undulating country the fictitious appearance 

 of a dun. Remarkably good sections are exposed the whole way up 

 this portion of the river. After the sand-rock has set in, the dips in- 

 crease by degrees until at the junction with the Lakrawdla sot the 

 angle is 6o° and the direction E.S.E. as before. Between here and 

 Kotri village it oscillates between 6o° and 55 and then once more 

 ( M2 j 



