GEOGRAPHICAL DISTRIBUTION, 6i 



the mica belt. The whole of the schists and the rocks to the west of 

 them are in turn intersected by one, or possibly two, series of dykes, 

 generally of olivine-free diabase, though some dykes are of beautifully 

 fresh olivine-diabase with well developed ophitic structure. Recent 

 formations, such as laterite, kankar and alluvium, conceal the older rocks 

 in most places, so that opportunity for geological observation is very 

 limited. The general strike of the roeks varies from west-north-west 

 to north-north-west. 



South of the Penner river the rocks of the schist complex are 

 largely well-foliated biotite and hornblende-schists, at times containing 

 nearly enough felspar to be called gneisses. Talcose and chloritic 

 schists are chiefly confined to one band dipping at high angles, and 

 extending past Saidipuram and Orupalle to the north-west for a con- 

 siderable distance. These latter schists are generally garnetiferous 

 and frequently kyanitiferous, whilst the talcose band near Saidapuiam 

 becomes massive in some places and is then of value as a potstone. 

 Very prominent, but really of relatively small volume, is a series of 

 narrow quartzite bands, which, having resisted the denuding forces 

 better than the surrounding softer schists, stretch across the country 

 in conspicuous narrow ridges, often lending variety to an otherwise ill- 

 decked landscape. North of the Penner, biotite-schists and quartzites 

 give way to the hornblende-rocks, which are on the whole more 

 massive than to the south. 



East of a line joining Chaganam (i4°i3'; 79°45'), and Yerraballe 

 (15°; 7L)°4o') pegmatite masses in the schists are of frequent occur- 

 rence, though no penological or structural feature has been observed 

 sufficient to account for the abundance of the mica-bearing rocks in 

 the eastern half of the schist complex and their complete absence in 

 the western half. 



The younger rocks between the schist complex and the coast are 

 principally alluvium and blown sand, with a narrow band of Cuddalore 

 sandstone and an occasional exposure of Rajmahal plant beds. The 

 schist complex is mica-bearing practically up to the western boundary 



E 2 ( 51 ) 



