IZ FOOTE : GEOLOGY OF MADURA AND TINNEVELLY DISTRICTS. 



than granite gneisses. The general dip of the rocks over the Tirnman- 

 galam plain is north-easterly, corresponding to that of the overlying 

 granular quartz rock. The same prevalence of north-easterly dip is 

 to be noted in the various outcrops of gneiss, which show through the 

 regur plain to the south-eastward between the valleys of the Gondar 

 and the Vaipar. The principal outcrops here noted will be referred to 

 at length further on. 



8. The lower granular quartz rock group forms a low rocky ridge, 

 Lower granular quartz about 3 miles southward of the great Naga- 

 rock, or Kokulam group. ^QsA^x ridge which makes so conspicuous a fea- 

 ture in the landscape around Madura city. I have named it after the 

 village of Kokulam (Cokolum) which stands close to where the ridge is 

 crossed by the high road from Tirumangalam to Sholavandan. This band 

 of granular quartz rock, though of no gi'eat thickness, forms a very well 

 marked ridge, traceable, despite some gaps, for many miles. To the north- 

 westward it was observed maintaining its individuality and its parallelism 

 to the Nagamalai for several miles, indeed as far as the eye could reach 

 from the new high road crossing the Nagamalai from Sholavandan to Tiru- 

 mangalam. At a point about 2 miles north-west of the Sikandar Malai 

 (Skanda Malai) the ridge trends southward and then eastward again and 

 passes southward of the last named hill, and then after trending south-east 

 for some 3 miles changes its strike to north-east by east, and after a couple 

 of miles is lost under the alluvium of the Vaigai at a point 4 miles due 

 south of Madura. Owing to the coarseness of the rock, which is a typical 

 granular quartz rock, the dip of the bed is not easy to recognise close at 

 hand, but when seen from a little distance the dip is perfectly obvious, 

 indeed strikingly clear. The question of the continuation of this formation 

 on the north bank of the Vaigai river will be referred to again further on 

 when dealing with the overlying Nagamalai granular quartz series. 



5. The middle granitoid gneiss group. — Immediately overlying the 



Middle grauite gneiss, lowest granular quartz series is a well marked 

 or Sikandar Malai group, y^^^^ ^f typical granite gneisfi, especially well 



seen in the Sikandar Malai 'Sh miles south-west of Madura. It shows 



( 1^ ) 



