900 THE GEOLOGY OF THE NANDBWAR MOUNTAINS, 



grained, greenish-grej rock, which becomes red on weathering. 

 It forms the whole plug of Deriah Mountain. 



Texture holocrystalline, medium-grained and even grained, 

 with trachytic habit. 



Composition : the main constituents are anorthoclase felspar 

 and sanidine. In addition we have ?egirine in broken fragments 

 of idiomorphic crystals; arfvedsonite in the characteristic aggre- 

 gates; a little brown pleochroic amphibole intergrow^n with arf- 

 vedsonite; heematite, and very sparingly quartz. 



Name : Arfvedsonite ^girine Trachyte. Magmatic name, 

 Phlegrose (cp. Tables i. and ii.). 



N.53. Loc: around Deriah Mountain. 



Handspecimen a highly porphyritic and vesicular rock. The 

 vesicles contain numerous decomposition-products of a zeohtic 

 nature. 



Texture holocrystalline, porphyritic, w4th a hyalopilitic base 

 which is partly cryptocrystalline. 



Composition : the phenocrysts consist mainly of labradorite 

 felspar of the composition Abo An .3; they are idiomorphic and of 

 prismatic habit, and are twinned on the Carlsbad, Albite and 

 Pericline laws. Amongst the phenocrysts must also be included 

 some very corroded phenocrysts of albite, oligoclase and ortho- 

 €lase which are studded with inclusions of glass and apatite. 

 Those of albite and oligoclase are intergrown with orthoclase at 

 the centre. Felspar forms also the main bulk of the base, in 

 the form of microlites of acicular habit; these needles possess 

 straight extinction and have a refractive index lower than 

 Canada balsam; they are for the most part untwinned, but in 

 rare cases they possess Carlsbad twinning; they may be either 

 orthoclase or albite. Interstitially we have a brownish material 

 which, under the high power, is partly resolved into minute 

 round globules. The rest of the brownish material consists of 

 glass and iron ores including some idiomorphic magnetite grains, 

 secondary haematite and limonite. 



Name : this rock must be referred to the trachyte family, 

 though from the excess of plagioclase in it, it furnishes a link 



