90 GEOLOGY OF TRICHINOPOLYj &C. [ChAP. IV. 2. 



2. Magnesite Veins, &c. 



No more striking example of the extreme degree to wliich meta- 

 morphosing agencies have affected the rocks of this area can be 

 adduced than those observable in various places in connection with con- 

 siderable developments of rocks rich in magnesia ; more especially in con- 

 nection with talcose and chl critic rocks ; more rarely, and in a rather less 

 degree, with amphibolitic and other hornblendic rocks. The results of 

 such metamorphic action appear in the formation, locally, of innumerable 

 veins of magnesite, or carbonate of magnesia, traversing what would 

 appear to be the original joint fissures of the rock, which in itself is greatly 

 altered, having become very earthy in texture, and assuming often a 

 very cindery and burnt-up appearance. 



Such is eminently the ease at the so-called '' Chalk Hills,^^ 5 miles 



north-west of Salem, by far the largest and best 

 The " Chalk Hills." 



known of the various areas over which these mag- 

 nesite veins occur ; and a description of this area will give a tolerable idea 

 of the main features observable in all the cases where these phenomena 

 were noticed during the progress of the survey. 



The area over which these alterations have taken place, in the case 



of the Chalk Hills, is one of very considerable 



Extent of area. , „ , ,-, 



extent, as may be seen on reierence to the map ; 



it occupies a space, or rather two spaces of irregular shape, about 3^ 

 miles north of Salem, and covers, roughly speaking, about 10 square 

 miles of ground. The extreme western point on the southern space to 

 which the magnesite veins extend lies a few hundred yards south-south- 

 west of the south angle of the Mancoopum tank (Maungoopay of the 

 map) . The veins all appear running along and across a long ridge from 

 one-half to three-quarters of a mile in width, which extends, with slight 

 undulations, in an east-north-east direction, to within half a mile of the 

 western base of the Nagra MuUay, a conspicuous hill lying due north of 

 Salem town at a distance of about 3 miles. The southern edge of the 

 northern and larger of the two magnesite-vein-bearing spaces runs parallel 



( 312 ) 



