GNEISSIC ROCKS. 11 



have been examined, for the greater part of the low country occupied by 

 gneissic rocks in South Madura and North Tinnevellj is covered with a 

 wide spread deposit of black cotton soil (regur). The few isolated 

 outcrops of the gneissic rocks met with are far from sufficient to allow 

 of any correlation of even the great bands of granular quartz rocks which 

 form such conspicuous hills and ridges around both Madura and Palam- 

 cotta. Nothing more can at present be said of their relationship than 

 that ii; is possible that both sets of beds may represent one and the 

 same series. The great regur spread which forms the cotton district of 

 Tinnevelly divides the two metamorphic areas so thoroughly that they 

 must be considered and described separately. 



{a) The metamorphic Area of Madura District. 

 So far as examined at present the gneissic rocks in the Madura district 

 may be divided into six groups — 



6. The upper granular quartz rock — AUagir'i group. 

 5. The upper granitoid gneiss — Melur group. 

 4. The naiddle granular quartz rock — Nagamalai group. 

 3. The middle granitoid gneiss— Sikandarmalai group. 

 2. The lower granular quartz rock — Kokulara group. 

 1. The lower granitoid gneiss— Tirumangalam group. 



1. The lower granitoid gneiss group, the lowest of this series. 



Lower granite gneiss, i^ the set of beds Occurring in the great plain 



or Tirumangalam group, f^^.^j^g ^he Tirumangalam Taluq, which is 



bounded on the east by the lateritie and alluvial formations. The 

 northern part of the Tirumangalam plain is largely covered with red soil, 

 but south of Tirumangalam town, cotton soil (regur) is met with every- 

 where, and allows but little of the subrock to be seen . The prevalent 

 form of rock is granite gneiss, important outcrops of which are seen to 

 the north of Tirumangalam at Karadikal (Kurdykul), along the south 

 side of the great Mulang Kulam (tank) and at Nellayur to the north- 

 east. Again to the south-east and south outcrops of very typical gra- 

 nite gneiss are to be seen along the valley of the Goadar and to the south 

 in the Chevvur Kotai hill. The other outcrops are less characteristically 

 granitoid in character, the rocks seen being rather banded massive gneisses 



( 11 ) 



