43 GEOLOGY OF THE SON VALLEY, ETC. 



cut down, and if the Son had not previously been evolved as a 

 river carrying off the drainage of the country south of the main 

 area of the upper Vindhyans, it then cut its way back along the 

 outcrop of the soft beds of the lower Vindhyan series and diverted 

 the drainage to the eastwards. 



Against the supposition that the present course of the Son is not 

 of geologically recent origin, and due to diversion of drainage, must 

 be placed the absence of any considerable tributary joining it from 

 the north. Had the present valley of the Son been an ancient main 

 drainage channel, antecedent to the last great uplift, it is difficult to 

 understand how no valley had been formed on its north side ; yet 

 at the present day the tributaries from the north are few and in- 

 considerable. 



The most important is probably the Ghagar, which joins the Son 

 near Chopan, issuing from the upper Vindhyan 

 EtesSi? The U Ghag S a°r! area near Markundi, and this bears the impress 

 of being a new stream which has cut its way 

 back from the Son. At Markundi the Vindhyan scarp bends south- 

 wards and cuts across the axis of an anticlinial ; the Kaimur sand- 

 stones, too, are here divided by a band of shales, the Bijaigarh shales, 

 along whose outcrop the Ghagar flows for some distance in from 

 the boundary of the upper Vindhyans, in a deep-cut steep-sided 

 valley showing every sign of erosion being in active progress at the 

 present time. The stream breaks through the scarp of the upper 

 Kaimur sandstone in a narrow steep-sided gorge, and its upper 

 waters drain a fairly large area on the plateau of the Kaimur sand- 

 stone. 



The lower part of this valley presents none of the features of an 

 old valley ; it appears to have cut its way back along the outcrop 

 of the Bijaigarh shales and then through the scarp into the plain, 

 covered by recent deposits above it. The features would not be 

 incompatible with the valley having been in existence prior to the 

 last great uplift, the signs of erosion would then be due to this 

 small stream not having cut its bed down at the same rate as the 

 ( 4« ) 



