STRATIGRAPHY. 3 1 



that the deposits of this age are not in their original relation to 

 the older rocks they were deposited upon, but have been subjected 

 to a certain amount of displacement. 



The boundaries are consequently faulted in a sense, but not in 

 the ordinary sense of being determined by faults altogether posterior 

 in date to the accumulation of the beds they cut ; they are rather 

 of the nature of boundaries of original deposition ; that is to say, 

 their gradual development led to the formation of the hollow in 

 which the Gondwana beds were deposited. At times deposition 

 more than kept pace with the formation of the fault and the deposits 

 spread over it into the upthrow side to the north, as is shown by 

 the few small outliers still found close to, but north of, the main 

 boundary. For the most part, however, the deposits can never 

 have spread beyond the fault scarps which bounded the area of 

 deposition, and the present limit of distribution of the Gondwanas 

 must be very much the same as their original limit of formation. 



It will be seen from this that there have been two great periods 



Afresh period of dis- of tectonic disturbance in this region. The 

 turbance. fi rs t was the Vindhyan period of mountain 



formation by compression, the second is the Gondwana period of 

 surface faulting, unaccompanied by compression. These two systems 

 of disturbance appear to have been completely independent of each 

 other. The faulting of the Gondwana period, even within the area 

 of the map attached to this memoir, can be seen to obliquely truncate 

 the broad area of the transitions, and further west the upper Gond- 

 wana boundary crosses the whole width of the lower Vindhyan out- 

 crop and rocks of that age are found in close proximity to, though 

 not in actual contact with, the upper Vindhyan sandstones. 



This means that the system of disturbance by compression of 



the Vindhyan epoch had completely come to an 

 Not of compression. 



end and the mountains of the Vindhyan epoch 

 had been lowered by denudation and perhaps by actual subsidence, 

 when the new system of disturbance set in. This, so far from being 

 one of compression, must have been accompanied by an actual 



( 3' ) 



