DELHI QUARTZITE SERIES. 



105 



been derived. An irregular net-structure is all that suggests olivine. 

 It polishes to a dark-green, handsome rock. 



It seems quite a plausible theory that these outcrops indicate 

 a peridotite mass, situated somewhere in this area, and originally 

 intrusive along the " gape " of the quartzite rocks at the angle 

 of the knee-bend, and from which all the other siliceous, dolomitic 

 and magnesitic material originated by secondary changes such as 

 are common to ultrabasic peridotite rocks. 



Another interesting phase of this band of rocks becomes manifest 



Siliceous, ferruginous m tne moderately wide arm going towards 



and nianganiferous Vartha from the direction of the knee-bend. 



This constitutes a fairlv marked intermediate rid<>ie 

 between the two flanking Delhi Quartzite ridges, which have a steadv 

 dip of about 50° S.W. (text fig. 19). The width of this intermediate 



VARTHA 



N.byE. 



At inert/ Usee?, band. 



Fig. 19. 



S.bvW. * 



ridge is \ mile ; and the whole of it, as exposed immediately south 

 and south-east of Vartha, has the quartzite altered and permeated 

 by drusy cavities which give it a vesicular, slag-like appearance. 

 Exposures are numerous enough, but the hill is simply a heap 

 of disintegrated blocks and fragments thrown about at random, 

 though approximately in situ. Whilst most of these are highly 

 siliceous and gangue-like, such as specimens Nos. 

 are ferruginous and nianganiferous, such as 

 and become dark in colour, and contain within 

 crystals of (?) braunite and dusty pyrolusite 



2 



I B&J 



2 9 

 4 3 8" 

 2 '.) 

 440' 44 1 



the druses minute 



2 g 



44 1 



others 

 "(12428), 



as in 



Others, 



again, still more rarely found in solitary lumps here and there 

 appear considerably impregnated by black manganese ore which 

 shows in the thin section as opaque dots, blots and irregular 

 areas. The better specimens of this richer rock, however^ £A 

 (12429, PI. 13, fig. 5), did not yield more than about 7 per cent, of Mn 

 when analysed by my colleague Mr. H. Walker, in the Geological Survey 



