144 RANIGANJ COAL FIELD. [CHAP. VIII. 



within a portion of a Geological Epoch, so, in this case, the mere fact 

 of some dykes having slightly preceded the others, by no means proves 

 them to have had a distinct origin. The most careful examination was 

 devoted to an endeavor to trace out a supposed case of a distinct series 

 of dykes, but the conclusion was that, with the exception of those already 

 referred to in the Lower Damtidas, all were of the same general age. 

 As regards the Geological age, there appears good reason for sup- 

 posing that these intrusions may have been con- 

 Geological age of dykes. ; . , 



temporaneous with the great volcanic outbursts, 



of which evidence exists in the Eajinahal Hills. The dykes are cer- 

 tainly newer than the Panchet rocks, which they traverse in abund- 

 ance, and they are also newer than all the faults of the districts. 

 Now, however much evidence there may be of faulting and dis- 

 turbance preceding the Eajmahal period, the rocks belonging to that 

 formation have, in the district where alone they occur in Bengal, 

 scarcely been moved from their original horizontal position ; and 

 faults are very rare amongst them. It is probable that a period 

 of elevation and of great and long continued disturbance was con- 

 cluded in Bengal by the outbursts of lava now forming the range 

 of hills which stretches from the neighborhood of Soory to the banks 

 of the Ganges. 



No evidence of later volcanic action is known to exist in any part 

 of Bengal. The circumstance of scarcely any disturbance having 

 taken place at a more recent period is, in itself, strongly in favor of 

 the belief that the trap dykes of the Damuda country are not newer 

 than the lava flows of the Eajmahal Hills ; for had volcanic action 

 taken place, it would probably have been either preceded or accom- 

 panied by disturbance. If, therefore, it be conceded, that the age of 

 the trap dykes is not newer than that of the Eajmahal rocks, the period 

 during which they might have been formed is reduced to a com- 

 paratively small range. 



