NtJRPUR PLATEAU. 19S 



the two glens have a certain amount of stratigraphic resemblance ; from 

 this it may be inferred that similarity of conditions induced the denuda- 

 tion to follow certain lines. 



The streams in the Nilawan drain by far the largest part of the 



Niirpur plateaUj notwithstanding which the struc- 

 Drainage. 



ture of that plateau seems to indicate the former 



existence of an up tilted rim or edge along the whole of its southern side, 

 which must have been broken through in order to allow the drainage to 

 escape. This might have been effected by a fissure^ coinciding with the 

 general course of the glen being either left open or filled with portions of 

 the superincumbent beds, easily removable by denudation. Otherwise, 

 it can only be supposed that the superior height of the limestone and 

 underlying beds at the northern side of the plateau so influenced the 

 general disposition of the formerly overlying tertiary sandstones, &c,, 

 that a southerly drainage was initiated. The Saheti fault with its 

 subsidence of a couple of hundred feet obliquely crossing the direction 

 of this southerly outflow may have increased the tendency, or, if conti- 

 nued along the course of the future Nilawan, may have depressed a 

 portion of the tilted limestone rim, so as to decide the point at which the 

 erosion of the ravine commenced.'^ 



* In tlie case of tlie Sardi ravine, a longitudinal break coinciding with tlie axis of 

 an anticlinal, or what would otherwise have been an anticlinal curve, seems even more likely 

 to have taken place, for though the general inclinations are lower than down in the narrow 

 part of the Nilawan, there is a very general dip away from the edges of the excavation. 

 The drainage of the Sardi ravine also comes from a small basin to the northward, so small 

 that it seems quite disproportioned to the size of the gorge, and it is possible that much of 

 the eastern part of the Niirpur plateau may have discharged its rainfall into the Sardi ra- 

 vine before the streams to the northward through the soft tertiary sandstones were deepened 

 iSuflBciently to lead the water in that direction. Within little more than half a mile to the 

 westward of the latter ravine, a parallel stream to that within it runs due north for nearly 

 four miles, into the small basin above the head of the glen, and none of the water from 

 above the eastern edge of the Sardi glen escarpment, except some small streams about 

 Simbal, finds its way into this catchment basin. Here, too, the progressive destruction of 

 once overlying tertiary sandstones and clays may have led the denudation along the line of 

 the gorge ; but if this denudation had acted in the same manner as in many other cases over 

 the plateau country, it would have left the limestone surface of the anticlinal (if thia 

 latter existed) almost intact, instead of cutting a deep gorge right along the highest part 

 of it. The probabilities seem all in favour of erosion along fissures, or else of unequal 

 subsidence of the adjacent country around these glens, 



A 2 ( 193 ) 



