BETWEEN THE SON AND THE BANAS. 109 



Chapter VI.— COUNTRY BETWEEN THE SON AND THE 

 BANAS. (R. D. Oldham.) 



The area lying within the bend of the Son, where it turns from 

 a northerly to an easterly course, after receiving the Mahanadi, is 

 occupied principally by lower Vindhyan rocks. These are thrown 

 into an anticlinal fold to the north, and a synclinal to the south, the 

 two areas being separated by a fault. 



The bed of the Son, from the junction of the Mahanadi to where 

 it turns southwards towards Marai, is occupied 

 by a band of limestone which shows up very 

 conspicuously at the junction and at intervals on the banks down 

 stream. Southwards from this, along the Son, a series of shales and 

 sandstones are seen underlying the limestone just referred to. 

 They strike at first to N.-N.-W. and afterwards to S.-S.-E. and the 

 lime-stone band seen at the junction of the Mahanadi is seen once 

 more. It can be traced for only a short distance east of the Son, being 

 cut out by the fault which brings up the beds of the porcellanite stage. 



The fault is marked in the Son by a very sudden change of dip, 

 the 30 dip to S.-S-.E. of the limestone giving way to a vertical dip 

 in the beds of the porcellanite stage. This vertical dip soon bends 

 over to horizontal and then to S.-S.-E. again, the beds forming an 

 open synclinal in whose centre the limestone of the Mahanadi forms 

 a broad exposure. The porcellanite stage re-appears south of Ram- 

 garh and beyond them come the basal sandstone, which, when seen on 

 the bank of the Son, are thin, fine-grained, and difficult to distin- 

 guish from some of the quartzites of the transitions. 



To the east of the Son the two outcrops of the porcellanite stage 



Lower Vindhyan east are J° ined in the mann6r Sh ° Wn in the ma P« 

 of the Son. i n this area the rocks of this stage are full of 



fragments of felspar and quartz, giving them a very porphyritic 



appearance, but they are still well bedded and interstratified with 



shales. In the bed of the Son one bed of the northern outcrop, 



{ 109 ) 



