STRATIGRAPHY, 19 



furrows are not confined to the upper rounded surface of the 

 nodules, where they might be explained by a radial shedding of the 

 rainwater, but are also found on fractured surfaces where these 

 have been exposed to the weather for a sufficient period of time. 



The conditions of deposition of the rocks of the Kheinjua stage 

 seem to involve an alternation of subaqueous 



Conditions of deposition. . . , . . 



deposit in shallow water and subasrial accumu- 

 lation. The frequent ripple-markings may be due to the action of 

 either wind or water in motion, but the suncracks and raindrop 

 marks prove that the surface of the beds on which they are found was 

 exposed to the air and not covered by water. The conditions are in 

 fact those of extensive mud flats which, in the course of the period 

 covered by the formation of this stage, were sometimes converted 

 into shallow lakes, and sometimes exposed as mud flats on which 

 the material washed down from the neighbouring high ground was 

 slowly accumulated. 



The limestones have all the appearance of a subaqueous deposit. It 

 is difficult to see how regularly bedded limestones could be otherwise 

 formed, though it is also remarkable that neither in the limestones nor 

 in the associated shales has any trace of living organism been found. 



It is a noteworthy fact that these limestones, which suggest, 

 though they do not necessitate, tolerably deep water conditions of 

 deposition, are absent or very Mttle developed opposite the strip of 

 older rocks cut off by the line of Vindhyan outliers while they are 

 well developed on either side. This indicates that the region of 

 structural elevation lyinp between the main area of the Vindhyans 

 and the band of outliers, was even in lower Vindhyan times not only 

 a region of special structural elevation, but also a region of greater 

 surface elevation, over which the comparatively deep water condi- 

 tions to east and west were replaced by shallow water or dry land. 



The name of Rohtas was first l proposed by Mr. Medlicott in 



1870 for the group of limestones and associated 

 Rohtas stage. /y r , , 



shales at the top of the lower Vindhyans. The 



1 Manual of the Geology of India, 1st Ed., p. 78. 

 C 2 ( 19 ) 



