l8 GEOLOGY OF THE SON VALLEY, ETC. 



The name of the Kheinjua stage is derived from a range of hills 

 lying south of the Kaimur scarp at and be- 



Kheinjua stage. 



yond the western boundary of the Rewah State 

 in the Son valley. It appears to have been first used on the field 

 maps of Mr. W. L. Willson in 1S72, but the first published appear- 

 ance of the name was in 1895. 1 



The area occupied by the rocks of the Kheinjua stage was sur- 

 veyed by Mr. Datta who has written the detailed description of the 

 subdivisions of this stage printed as Chapter IX of this memoir. 

 The remarks on the lithology of the rocks of this stage will con- 

 sequently be restricted to generalities. 



The rocks of the Kheinjua stage are principally shales and sand- 

 stones. Some of the latter are purely arenaceous and sometimes 

 indurated to form quartzites ; but as a rule the sandstones are impure, 

 divided into thin beds, and freely ripple-marked on the bedding 

 surfaces. Limestones occur occasionally, and at the western limit 

 of the map there are three thick bands which thin out east of 

 Ramnagar and cease to be traceable as continuous bands. 



From near Ramnagar, eastwards to the neighbourhood of Mar- 

 kundi, occasional outcrops of limestone are found, and the bands may 

 sometimes be traced for a few miles, but there is no development 

 of limestone comparable to that west of Ramnagar. East of 

 Markundi and Chopan limestone again becomes a conspicuous mem- 

 ber of the stage, and Mr. Mallet's No. 7 attains a thickness of 200 

 to 300 feet. 



The uppermost member of the stage is a set of beds of shale 

 through which large rounded black calcareous concretions are scat- 

 tered. On the freshly fractured surface they appear to be compact 

 and homogeneous, except for traces of the original bedding travers- 

 ing them at right angles to their shorter axis. When weathered, 

 however, a series of furrows radiating from the centre indicate an 

 invisible septarian structure of radiating fissures, too fine and close to 

 be visible or to affect the fracture of the stone, but offering planes of 

 more ready solution of the material composing the nodules. These 



1 Rec, Geol. Surv. Ind., Vol. XXVI II., p. 145. 

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