NEEBUDDA DISTRICT. 163 



In addition to these causes, the trap dykes tend greatly to obscure any 



measurement of the thickness of the beds. Sub- 

 Trap Dykes. 



divisions (d) and (e) that is the flags and shales of 



the series occupy very considerable area in the Tawa valley ; they are 



often seen at the surface supported by the green muddy boulder bed, and 



generally overlaid by the massive sandstones described as (/) in our list. 



And an examination of the whole series, regard being had to all the above 



sources of error, leads me to estimate the thickness at not less than 700 



feet for the flags and shales (d) and (e). The difficulties of getting at the 



Thickness of upper thickness of the entire S rou P do not > however, end 

 dmsion - here, for the upper sub-division (/) still remains. 



Coarse thick bedded grey and brown felspathic sandstones form the top of 

 the lower Damuda series, as has been shown in both the sections above 

 given : these and even the beds below them, were disturbed and extensively 

 denuded before the deposition of the Mahadeva 



This has been denuded. 



sandstones, which here rest unconformably on them. 

 This unconformity is however often very slight, often so slight as to be 

 in short sections quite inappreciable. There exists, moreover, sufficiently 

 strong lithological similarity between the lowest part of the Mahadeva 

 sandstones, and this upper member of the Lower Damuda group thorough- 

 ly to obscure the junction between the two. 



The observer standing on the gently undulating flags, shales, and 



sandstone, of the Sonadi coal section, in the valley 

 Upper limit not clear. 



of the Bora Nuddi (see map) and looking towards 



Jamgur Hill, which is formed of Mahadeva sandstone, will be able 

 to perceive that the lower rocks (of the valley) are unconformably over- 

 laid by the massive sandstone beds of the hill ; but if he proceeds towards 

 the foot of the latter, he will find that these sandstones seem to pass 

 down into those of the low ground, and this so gradually, and impercep- 

 tibly, as to render it difficult, or often impossible, to determine the exact 

 position of the line which divides the two. 



This same feature is very strikingly displayed on the south side of the 



