36 GEOLOGY OF THE SON VALLEY, ETC. 



Chapter III.— PHYSICAL GEOGRAPHY AND ITS EVOLU- 

 TION. (R. D. Oldham.) 



The most striking physical feature of the area under report is 

 undoubtedly the great Vindhyan scarp, which 



Kaimur scarp. . 



also forms its northern boundary. This great 

 scarp, known further west as the Kaimur range, extends from Sasse- 

 ram in the east to the Narbada valley in the west, and throughout its 

 length rises abruptly to heights which range from 500 to over 1,000 

 feet above the low ground to the south. Throughout this length 

 too it forms the waterparting, except for a few small streams that 

 break through to the south and will be referred to further on, 

 between the drainage which finds its way northwards to the Ganges, 

 and that of the great strike valley of the Son and its westerly 

 continuations on the south. 



South of the Vindhyan scarp comes the low ground of the Son 

 Son valley and hills to valle y occupied by rocks of lower Vindhyan age 

 the south. an( j deeply covered by extensive dust deposits, 



from which rise a number of prominent ridges, formed by the 

 harder beds of that series. South of this again comes a mass of low 

 hills, forming more or less parallel discontinuous ridges and trav- 

 ersed by a series of rivers running northwards across the strike of the 

 rocks of the transition systems which occupy this area. To the 

 south of this mass of hills comes the more open ground of the Gond- 

 wana area, at first distinctly lower than that occupied by the transition 

 rocks, but further south rising into high, flat-topped plateaux with 

 irregular scarped faces, similar in general character to those of the 

 upper Vindhyan area. 



The surface features are directly dependent on the structure 

 of the different areas and on the differential action of denudation on 

 the hard and soft beds of which they are composed. When the 

 stratification is horizontal or nearly so, we get flat-topped plateaux 

 surrounded by steep scarps ; where the beds are tilted at high angles 

 we get more or less continuous straight, and sharp-crested ridges. 



( 36 ) 



