^6 OEOLOGY OF TUICIIINOPOLY; &C. [ClIAP. IV. 2. 



of Pullypiitty village. The surface of the rock is every where so much 

 decomposed that no fresh piece could be discovered from which to judge 

 of its real nature. The matrix of the rock would appear to be horn- 

 blendic. 



Near to the Nagra Mullay, the appearance of this black rock sug- . 

 gested the idea of its being a dyke-like intrusion of a trappean rock, 

 but east of the PuUyputty nullah, it assumes the appearance of a very 

 coarse hornblendic schist, in which the major axis of the crystals lies in 

 the direction of the prevailing strike of the unaltered hornblendic rocks, 

 situated outside the area of action of the metamorphosing agencies, 

 whatever they may have been. In almost every place where this rather 

 protean black rock shows itself through the thick red soil of the PuUy- 

 putty valley, it is traversed by very numerous small veins of magnesite. 



Such are the more striking features observable over this very 



„ , . , ,. , . n singular and interesting tract of country ; our 



magnesite. conclusions as to the causes of these phenomena 



will be found further on, after the description of the other magnesite- 



bearing tracts of country met with during our survey. 



Proceeding southward from Salem along the high road to Trichi- 

 nopoly, we me6t, in the neighbourhood of Namkid (Namcul) , with a 

 series of great curves, well shown by the low ridges formed by the pro- 

 truding out-crops or basset edges of the strata, the most remarkable of 

 Avhich are thick beds of hornblendic gneiss abounding in dark red garnets 

 of all sizes. 



Following the curve of one of these conspicuous ridges, which lies 



of miles north by east of Valiaputty " Travellers^ 



Bungalow" and immediately south of the Moo- 



oonaickenputty tanks, are a number of small veins of magnesite, chiefly 



protruding along the line of strike. 



The ridge of coarse dark hornblendic and very garnetifcvous schist_, 

 on the south side of which the magnesite veins ai-e situated, shows a 



( 318 ) 



