COUNTRY NORTH OF THE SON. 135 



This sudden apparent unconformity will not be accounted for 

 either by an ordinary fault, however well this would explain the 

 rectilinear shape of the boundary and a number of other features, 

 such as the low, undecided dips, the beds dipping just as often 

 towards the boundary as away from it. Lastly, there is the fact 

 already mentioned that in the river near Tal a natural junction may 

 be observed between the gneiss and Barakars, the Talchirs being 

 absent. 



It need hardly be added that the supposition of an unconformity, 

 while it would explain the proximity of the various stages, would 

 still leave the question of the shape of the boundary quite unsolved. 



It is the consideration of these various peculiarities which has 

 led me to interpret the features observed as the result of a sub- 

 sidence contemporaneous with the deposition of the beds. During 

 the whole time that the subsidence lasted, it would seem that 

 different movements never ceased taking place along this particular 

 line, or at least along several parallel lines in very close proximity to 

 one another, which would account for the slight irregularities 

 observed, such as the natural junction of the Barakars near Tal. 



The description of the line of boundary may appropriately com- 

 mence with this exposure. 



The contact of the Gondwanas with the Archaean gneiss is 

 exposed at Tal in the Kandas river, just below its confluence with 

 another tributary from Kachra and Ponri. 



The Gondwana rocks are thick beds of sandstone with much 

 decomposed felspar, resting upon a sloping surface of gneiss. The 

 strike of the boundary at this particular point is 25 E. of N. The 

 dip is insignificant, not exceeding 4 . The strike of the foliation 

 in the gneiss is 70 E. of N. 



This natural junction is not in disagreement with the existence 

 of a fault, if it be conceded that the fault was partly simultaneous 

 with the deposition of the beds. 



Suppose a fault takes place before the deposition of the sediment- 

 ary strata has commenced. If it is on a land surface subjected to 

 ordinary conditions of atmospheric erosion, the wall of the fault will 

 not remain as a cliff, but will be simultaneously denuded. If the 



( 135 ) 



