

120 HOLLAND: GEOLOGY OF THE NEIGHBOURHOOD OF SALEM. 



are also arranged in definite lines and probably planes in the fel- 

 spars, but the want of idiomorphic outlines prevents their determina- 

 tion. For the quartz three sets of needles have been found to be 

 arranged as follows :— 



(a) parallel to the lateral crystallographic axes, and thus in the 



principal planes of symmetry. 

 (5) parallel to the vertical axis. 

 (c) parallel to the face of the unit rhombohedron and lying in 



the secondary planes of symmetry. 

 The needles lying in the basal (isotropic) sections of quartz 

 show straight extinction, but being thinner than the quartz in which 

 they lie the distribution of the axes of elasticity in such sections 

 could not be determined. 



Whenever the hair-like inclusions occur in the quartz and 

 felspar of these rocks, the hypersthene and other ferromagnesian 

 silicates show the ordinary schiller inclusions in the form of black 

 and brown rods and plates, whilst in the basic garnetiferous 

 varieties, the garnets also contain acicular inclusions ; these last 

 have been described in a separate paper. 1 



With regard to the other constituents of the charnockite 



Mineral composition of series > the au S ite is the ordinary pale blue- 

 the intermediate forms. green var i etv characteristic of these rocks, the 



hyphersthene is highly pleochroic and the hornblende, a strongly 

 pleochroic, brown-green variety. Opaque iron-ores, zircon, apatite 

 and biotite occur as accessories. Microperthitic structures and 

 u quartz of corrosion " are very common in the " intermediate " 

 members of the charnockite series. 



The ordinary massive and well foliated rocks are traversed 

 by acid, coarse-grained veins (contemporaneous 



Schlieren. ' . . . . . 



or segregation veins) in which there is often 

 a considerable quantity of titaniferous iron-ore. In other places 



1 R**., Geol. Surv., Ind. t Vol. XXIX (1896), p. 16. 



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