PETROGRAPHICAL NOTES. 6Q 



d* — L imestones. 



It seems doubtful how far any of the Bijawar limestones are truly 

 of derived origin, that is, derived from the desintegration or solution 

 and the re-deposition, or re-precipitation of previously existing 

 limestones. Rocks of this nature occur sparingly in the underly- 

 ing gneiss. They may be the accumulated remains of calcareous 

 organisms, of which all trace has been obliterated, or they may 

 have resulted purely from chemical precipitation, being derived from 

 the supersaturated calcareous springs that usually accompany volcanic 

 eruptions, and would be therefore related to travertine. Their 

 close association with the volcanic rocks renders this interpretation 

 very probable. They are frequently so rich in chlorite that they 

 become chlorite-schists. The latter are in all probability metamor- 

 phosed tuffs. The most important runs of limestone are generally 

 interbedded with these chlorite schists. Sometimes the limestones 

 are not in direct contact with any volcanic rock, as in the case of the 

 strata interbedded with jasper at Agori. Wherever volcanic rocks 

 are totally absent, as in the region examined about Chingo, there is 

 also a complete absence of limestone. 



They frequently form small elongated lenticular masses varying 

 in dimensions from a few inches to several feet, intercalated 

 between the divisional planes of the calcareous chlorite schists. At 

 other times they form thick continuous bands. One of the most 

 important amongst these may be followed continuously from Urangi 

 up to Kosai. It has already been mentioned in connection with the 

 description of the Vindhyans. It is quite possible that several of 

 the outcrops which run in parallel bands are repetitions of the same 

 rock due to folding, but a detailed survey would be necessary to 

 decide that point. 



When it forms lenticular masses amongst the chlorite schists, 

 the limestone is frequently somewhat fine-grained and is striped in 

 a direction parallel with the strike of the schists, showing bands of 

 white pink-grey or greenish and bluish tinge (specimen T ^ and T y-) 

 Sometimes it is coarser grained and saccharoid (specimen T M-). 



( 6 9 ) 67 ' 



