l6o GEOLOGY OF THE SON VALLEY, ETC. 



2 inches thick, of the siliceous shale could be traced for a few yards 



Dip-conformitv but no alon § the junction with a perfect dip-conformity 



gradual passage. with the over i y ; ng san dstcne, although in the 



character of the constituent materials the shale and sandstone were 

 sharply marked off, one being of fine argillaceous material, perhaps 

 somewhat siliceous, and the other purely arenaceous. 



Diholi. — At a point at the foot of the Kaimur scarp, north-west of 

 Diholi, is seen a section quite similar to the pre- 

 ceding, but here the limestone (Rohtas) is ex- 

 posed in addition, underlying the sub-porcellanic siliceous shales. 

 These shales are very well seen here, being light to dark grey in the 

 lower parts and rather finely laminated in the upper parts. The junc- 

 tion of the sandstone with these shales is as in 

 Rohtas with th? overlying the preceding section, but the contact of the 

 latter with the underlying limestone is not ex- 

 posed. The point of interest, however, here is that all the three sets 

 of beds, namely, the Rohtas, the suprajacent siliceous shales, and the 

 sandstone overlying the last, are all well exposed, exhibiting a per- 

 fect parallelism of bedding between one another. 



We thus find from these sections that while near Ginaor the sub- 

 What these sections porcellanic shales pass up into a shale which in 

 show# turn seems to pass into a sandstone, this latter 



shale is little developed by Tikat. Throughout the greater part of the 

 area in sheet 474 (/.<?., from Long. &2 to 82 20' ), the rim of the 

 upper Vindhyan basin seems depressed, and the Kaimur sand- 

 stone comes down to the level cf the alluvium of the plains. East- 

 wards of this point the Rohtas is again visible by the foot of the 

 scarp, but the siliceous shales are no longer traceable, being appar- 

 ently absent, the result being that the Rohtas is in direct contact 

 with the sandstone of the Kaimur scarp. These last two sets of 

 beds, however, exhibit a thorough dip-conformity throughout. 



From the sections recorded above we are thus, in conclusion, led 



Inferences from the £q infer 



sections recorded above. 



(i) That there is a passage from the Rohtas limestone into the 

 ( 160 ) 



