66 HUGHES : WARDHA VALLEY COAL-FIELD. 



This occurs naturally at the margin of every area of deposition, whe- 

 ther in a water-basin, involving depression for lateral overlap, or in an 

 alluvial plain by the simple growth of accumulation. Without the prefix 

 overlap, it is rather misleading to speak of this mode of relation of suc- 

 cessive formations as unconformity. 



Now the question is, which of these cases fits best to the observed 

 features of the Kamthi-Barakar contact ? We can at once pronounce 

 about the overlap ; it occurs freely, the Kamthis being often found rest- 

 ing on rocks older than the Barakars ; but I am unable to refer to a 

 single section showing distinct unconformable contact, or to show evidence 

 of the Barakars having once occupied ground where they are not now found 

 beneath the Kamthis. In other words, there is no direct evidence of a 

 pre-Kamthi denudation, with or without, disturbance of the Barakars. It 

 must be admitted that the ground is very covered, and good sections are 

 scarce ; but, on the other hand, it may be said that evidence of intervening 

 denudation between two deposits would not be limited to contact-sections. 



In the case of these borings we obtain what may be called internal 

 evidence, as compared with the mere mechanical evidence of unconformity. 

 If the concealed margins of the seam beneath the Kamthis were denuda- 

 tion margins, we might expect them to be like such outcrops now ex- 

 posed. We should touch coal at once, of something like the average 

 quality, having only suffered in the usual way from weathering ; and the 

 seam, or such portion of it as is left, should be something like an average 

 of the same portion as found to the deep. But it is not so ; the borings 

 show that these attenuated outcrops can never have represented an aver- 

 age section of the seam. We find shale, not deteriorated coal. Now this 

 is just what would occur along the original limits of accumulation of 

 coal-forming vegetation. 



Section VIII. — Kamthi Group. 

 In ascending order the next group of rocks is that to which the 

 name of Kamthi has been given. It is unconformable to the Barakars, 

 ( 66 ) 



