STRATIGRAPHY. 2J 



deposited ; but the place where these conditions prevailed was 

 away from, and probably to the south of, the present Kaimur-Rohtas 

 boundary. Lastly, we find that, in the outliers south of the Son, 

 beds of upper Vindhyan, though not necessarily of Kaimur age, are 

 in absolute unconformity to the lower Vindhyans, which had un- 

 dergone almost the whole of their present disturbance and been 

 exposed to great denudation before the deposition of the sandstones 

 of the outliers. 



The explanation of these anomalies is to be looked for in the 

 conditions of deposition of the Vindhyan system. 



An old mountain range. , , . . , A/r , f 



In the second edition ot the Manual 01 the 

 Geology of India 1 I showed how the boundary of the Vindhyans 

 towards the Aravalli mountains was precisely analogous to that 

 of the Sivvalik series and Gangetic alluvium towards the Himalayas, 

 and suggested that just as the Siwaliks and Gangetic alluvium were 

 Formed during the elevation of the Himalayas, and of the debris 

 washed down from those mountains, so the great Vindhyan system is 

 contemporaneous with the original elevation of the Aravalli mountains 

 and formed of the debris washed down from them while they were 

 still growing and a far more important mountain range than the relics 

 which remain at the present day. 



The Aravallis were probably not the only mountain range of that 

 period, and it is not too much to suppose that another range ran 

 along the southern edge of the Vindhyan area^along and south of the 

 present valleys of the Narbada and Son. In this case the peculiar 

 relation of the upper to the lower Vindhyans would find an easy 

 explanation ; they would naturally be conformable in the area of 

 deposition beyond the limits of the zone of folding and mountain- 

 formation, while within that zone the lower Vindhyans might easily 

 be compressed, elevated, denuded and then covered up by later 

 deposits of the same system ; just as we find the tertiary deposits 

 of the extra peninsular hills showing great unconformable breaks on 

 one section and on another a perfectly conformable sequence. 



1 Page 103. 



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