110 GEOLOGY OF THE SON VALLEY, ETC. 



which is specially porphyritic, forms a small waterfall, and on the 

 broken edge of the bed it is seen to have an obscure columnar 

 jointing. 



The basement beds, traced to the east from the Son, thicken 

 considerably and soon form a conspicuous ridge, which is interrupted 

 by an oblique fault about a mile east of the Son, and the gap so 

 formed has been utilised by a small tributary of the Son. East- 

 wards of this gap the sandstones thicken and the ridge increases ia 

 height till it runs into the hills west of Tikhua ; here it forms the 

 northern flank of the hills and is apparently cut off by a fault. It 

 is by no means certain that the rocks of this horizon are not 

 represented in the southern and south-western portion of the area 

 which has been included in the Kharara outlier of the upper 

 Vindhyans. 



Conglomerates are rare in this outcrop of the basement beds* 

 Some pebbly bands are seen at the base of the section in the stream 

 which flows down from Panrui, and in that which flows past Margarh,, 

 where there is a thickness of fully 1,000 feet exposed. 



To the north of the basement sandstones there is only a narrow 

 band of shales near the Son, but in the plain east of Margarh the 

 exposure broadens out very greatly. The area occupied indicates a 

 great thickening and the few exposures seen have all tolerably high 

 dips, indicating a good deal of disturbance, but there is no indication 

 of the existence of any rock belonging to one of the higher stages. 



North of the line of fault there is a broad open anticlinal of beds 

 belonging to the lower part of the Kheinjua stage, whose axis runs 

 from one to two miles south of the Son. The rocks exposed consist 

 of shales and sandstones, the latter frequently ripple-marked and,, 

 where tolerably pure, indurated into quartzites. 



The neighbourhood of Marai proved more difficult to map than 



Neighbourhood of an y other part of the area surveyed, and its 



Mara,# interpretation still remains doubtful as regards 



some points. To the north-east of Marai the basement beds of the 



( "o ) 



