CHAPTER VI. 



Lower Gondwana. 



Bardkar Group (Damuda Series). 



The coal-bearing rocks of the Rajmehal hills possess the same 

 general lithological characters as have been found in the Damuda coal- 

 measures wherever they occur in India. In no one section in these hills is 

 the thickness seen greater than 500 feet; in places it thins out to nothing, 



the super-imposed Dubrajpur beds, or trap, as the 

 Thickness. A 



case may be, gradually lapping over on to the gneiss 



or v Talchirs. These diminutions of thickness are attributable to two causes. 



The first, and more obvious one, being denudation ; the second being the 



original irregular configuration of the metamorphic rocks, the higher 



portions of which were not covered until the valleys had been filled up. 



Between the Damudas of the northern portion of the area and those 



Two groups of Damu- °^ tne southern there is a considerable contrast in 



das ' lithological characters; but both of them find 



their representatives in different portions of the complete sections which 



occur in other parts of India. 



In the north, i. <?., north of the Chuperbhita pass, the principal rocks 

 seen are coarse, highly felspathic friable grits with white argillaceous 

 beds and a few thick seams of inferior coal. In the south, the alterna- 

 tions between fine sandstones, conglomerates, blue argillaceous shales, 

 carbonaceous shales and coal are rapid and distinct ; in other words, the 

 rocks present the characteristic appearances of normal Barakars of the 

 Raniganj field. 



Without reference to other localities it is difficult to determine 

 with which of these two rests the probability of being prior in the 

 period of its deposition. Whereas in the southern area we have Talchirs, 

 d ( 179 ) 



