IIG GEOLOGY OF TRICHINOPOLY, &C. [ClIAP. V. 



Ill a granite vein at the village of Vapanuttom (3 miles from 

 Namkul), many of the quartz masses show very perfect cavities that had 

 apparently been occupied by rather tabular-shaped crystals of felspar. 

 Some of the cavities are fully 2 inches in length. Another small vein^ re- 

 markable for containing occasionally nearly perfect (pseudomorphic) prisms 

 with terminal pyramids of bright silvery-grey mica_, occurs on the south 

 side of the low hills lying north-west of Vapanuttom^ which forms the 

 apex of a great curve in some of the hornblendic and garnetiferous beds 

 belonging to the great Kolymullay-Tullamullay series. 



Prisms of black tourmaline or schorl were met with in great numbers 

 in a quartz vein having a north and south course, 

 and lying immediately south of the village of 

 Aulthromputty^ in the great Oopillipooram valley. 



Obscure and badly shaped crystals of the same minei'al occiir in 

 small veins exposed by a nullah running into the Guddalam river, close 

 to the village of Vundaraddi, in South Arcot. 



The large granite vein of Colingaputty, already alluded to as con- 

 taining enormously large crystals of felspar, contains also large plates of 

 coarse blackish-green talc. 



Besides the accessory minerals already named, none else were observ- 

 ed in the granite veins but garnets and grains of magnetic iron. 



Graphic granite occurs in the central part of two large granite 

 veins, the first of which is situated on the south 

 side of the crystalline limestone at Naivaillie, 

 and the second, in the great vein extending from the Tipramahdevy hill 

 to the travellers' bungalow at Valiaputty. In both cases the outer part 

 of the veins consists of common coarse quartzo-felspathic granite, without 

 any trace of the graphic arrangement. 



A very large but only slightly exposed granite vein runs from a 

 little south-west of Darmahpoor as a ridge across country in a direction 

 to near the top of the Toopoor Pass, a point lying beyond the confines of 

 ( 338 ) 



